Dad (93) still has his checkbook & gives money he can't afford to my leeching brother. I am POA, can I take my Dad's checkbook?

Not unless he is incompetent. If he can give money to brother than you don't need to foot half the bill. Tell him that. Its not fair you are giving only to have brother taking, If Dads IL supplies his meals not much more he needs, Utlities shouldn't be much. Does he participate in outings, use a bus to get around? I would leave what he needs in spending money and use the rest for rent and utilities, Then there is nothing for brother.

I was drawn to your question one of the reasons being the heading that I see in the list of questions is..."he does not have dementia"...now I see that nowhere in the question above and I do not see it in your profile. So I do not know where this information comes from.
but here goes...
If he does not have dementia you can not do anything to his accounts. (Although you might be able to if you are listed as being on the account and can withdraw money. write checks, close the account, things you could do with your own account.)
You say "age related decline" I think once a person starts making bad or I should say poor decisions it begins to move from being age related decline and more to the "dementia" realm. His next medical check should include testing for dementia, most doctors are doing that on a routine basis now if for no other reason but to get a baseline so determine how one changes from year to year.

I also think that you should not be paying for half of the Independent Living or Assisted Living bill. If he does not have the money you should begin the application process for Medicaid now. And keep in mind ANY money he has given to your brother will be looked at closely and may dramatically effect the possibility of Medicaid. Is your dad a Veteran? If so look to the VA for any number of resources as well. This is also a discussion you may have to have with your brother that he may either have to pay back money that was given to him and tell him the "well has dried up" and he needs to find other resources for his cash infusion.

Tell your dad you can no longer afford to subsidize his rent.

How do you know that his cognitive skills are intact? Has he had a real workup?

I took in my 89-year-old mother after she was diagnosed with cancer. For at least a decade before that, she sent my mooching younger brother and his wife (who won't work much and never visited her) $600-$900 per month from her meager pension and social security income. She gave them all of her savings, allowed them to charge more than $8,000 on her credit card, and wasn't eating well, buying clothes, or going to the dentist.

After she moved in, I noticed she couldn't manage her checkbook and was suffering more mental decline than was visible during visits. We went to the bank and had my name added to Mom's checking account. I put a stop to the payments to my brother and explained to her that she'd soon need in-home care and she had to save her money for that as brother certainly would not be able to help. She didn't object much, so I think she knew on some level that my brother was taking advantage of her. Sending him money had just become a habit, like paying any other bill.

Guess what? Eighteen months later, my brother and his wife are managing just fine (though he still complains to Mom about money in every telephone conversation). Mom has been able to treat herself to some clothes and go to the dentist. She has accumulated enough money to cover at least some of her upcoming nursing needs.

Moochers are manipulators, pure and simple. The sooner they are stopped, the better for our parents.

I vote take it away, one way or another. He doesn't have the money. You are subsidizing him. Stop the insanity.

Only if your dad is competent. But why are your funds being used? If dad has money, he should be paying you, not your brother.  Have you insisted on this as a matter of honesty and fairness?

This is a tough one. When my dad was in IL the only thing he needed money for was trips to the grocery store. He used his credit card for that. I am his POA and handled all his bills through automatic draft and also writing any checks.
I don’t see why he needs checks.
Sounds like your brother is a bit of a mooch and I’m not sure why you pay half but obviously dad has spending money enough to give to the moocher. I’d say to dad "let me keep Your checkbook safe and to pay bills with and I’ll give you cash for incidentals". Also that he can use a credit card but ONLY if you deem that safe.
On another note, I don’t trust brother. Be sure dad's credit reports are frozen with the 3 credit reporting agencies if you haven’t done that yet. Congress finally made that free. That way brother, nor anyone else can take out loans or steal his identity. Set up an account with social security and the IRS so that those too can’t be used by someone else. There are so many scammers and fraudsters out there. Be sure your dad knows about the scam callers out there and to just hang up. My sister's MIL who is very intelligent was scammed out of 13,000 by a caller. It was unbelievable she fell for it but it happens. If he uses a computer be sure security and firewalls are in place. So much to think about.

I'm curious as to how your POA reads, as generally as POA you can manage all allowed affairs, until the POA is revoked, if he is not competent (medically proven), he cannot revoke it. Is your name on his account?

If you are having to pay partial support, brother should be stopped entirely.
This has to be causing friction and bad feelings, You should notify the brother in writing, laying out your level of support, and informing him that he is now misusing funds both Dad's and yours. As a first step.

There are other choices, but it might involve accusation of elder abuse.
You should make a ledger of all disbursements ffom Dad to brother

Avoid conservator ships /guardian ships, unless you fully understand consequences.

If Dad is still competent you should update Will Living Trust, POA, and Advance Health Care directive. Before it is too late

How did it come about that you’re paying half the IL rent? Does Dad know or what? Regardless, by doing so you are subsidizing brother by subsidizing Dad. You’re enabling them both — that’s usually what happens to the nice person when there is a manipulative person in the equation.

If Dad is of sound mind, then sitting with him to figure out his IL expenses without your money is in order. If he isn’t of sound mind, then he won’t be able to be in IL much longer, and his expenses will rise when moving to AL.

Has he always had inability to meet financial needs, since you are paying have the rent? If not, his executive skills are starting to go. Does he do the yearly Medicare physical? If he doesn’t, he should to assess for future needs. Talk to his doctor about his changes if there are any. If you have the finances and want to cover his costs the next 10 years. (Many are living past 100) let it be. If not your other route is to stop supporting him, although that might just empty his funds sooner. Most important is to talk with him if possible to get his understanding of his finances. Perhaps he has the idea, he is not going to be here much longer, and he can’t take it with him, so why not help his brother. He also appears to think you have unlimited funds, that he does not mind you paying his way.