Mom has multiple county violations. Should someone call on her, am I responsible?

Let Mom get the violation. Make the Township aware that the junk is brothers that he has been asked to remove it and he won't. Then ask if Township cleans it up what would it cost. Then ask if the bill can be sent to brother if they agree to then tell brother if he does not get the junk off of Moms property he will be billed ____ amount of money by the Township. If he doesn't pay it, a lien will be placed on his house. At the point that Mom gets violations she can have a lawyer send a letter saying that brother must get the junk removed from Moms property by a certain date. If not done, she will get rid of the junk and send him the bill.

You should call the cops on your brother for illegal dumping.

If mom is cognizant, able to care for herself, able to make decisions for herself then your POA/ DPOA is not yet in effect. She can make her own decisions.
If she is aware that she may get fined and if she is willing to pay the fines then that is on her.
If she does not want to pay the fines but does not want to get the yard cleaned up simply because she does not want to upset her son then she can ask her lawyer to send a letter to the son demanding that the items be removed by a particular date and if they are not removed they will be hauled away and the bill sent to the son. This way the letter is from the lawyer, not mom.

bearcountry, no you are not responsible for your Mom's yard. Sounds like Mom is able to take care of herself, plus she is able to drive. Your helping out is no different than any grown child stopping by to visit with their parents, helping out here or there.

The Power of Attorney doesn't start until your Mom is unable to make good decisions for herself, or is unable to take care of herself.

In some places, the City/Town/County will send a certain number of violations. If nothing get done, then the City/Town/County will give notice that they themselves will come onto the property and remove the items. Then the homeowner will get a bill. The bill will be pricey.

If I were you, having POA, I'd use mom's money, hire a junk removal company, and have all that crap hauled out of her yard and taken to the dump. I don't know the answers to your questions about whether or not you're responsible for her as her 'legal caregiver', etc. But having POA for her would be enough, imo, to haul that clutter out of there, considering she has all these violations (or may have them if a neighbor calls to complain, I'm not sure which, based on your wording). If your brother doesn't like it, he can lump it. He shouldn't have brought all that stuff over to mom's yard in the first place, and he's acting like a bully to boot, so too bad if he's angry that you did the right thing by getting rid of it. I doubt you're legally responsible for having her yard cleaned up, either, but it seems simple enough to have it done and finished, once and for all. Because SHE is responsible for these violations (or if she eventually gets them), and as her POA, the headache is yours in the end anyway, so that's my take on the matter.

Good luck!