My mother is showing obvious signs of dementia such as short term memory loss. Her husband (my step dad) will not share her diagnosis with children.

You can call social services for her county and ask a social worker about the possibility of emergency guardianship. I worry that if you call APS I'm not sure if they'll say who reported them, and if you can't be anonymous, then your step-dad might stop all contact with you.

If you feel desperate about the situation you can plan to rescue her by going over there with your sisters and their spouses/boyfriends with food and keep him distracted while someone packs some of her things and ushers her out of the home. This only works if she's cooperative. Just because they're married doesn't give step-dad the right to hold her hostage. You can assure her it is only temporary while step-dad "goes to treatment" or whatever story will get her onboard,

This is what my cousins did for their Mom, married to my abusive Uncle. The 3 sons finally got fed up and took a risk and removed her right in front of my Uncle. He's a big angry scary dude but was intimidated by their determination and outnumbered by my brave cousins. My Aunt had dementia and was being totally neglected by that a-hole.

Then someone is going to have to deal with any money issues (like joint bank account so step-addict doesn't drain it) or valuables, etc. Put a credit alert on your Mom. Get a restraining order for the jerk. It's a lot, but it's your Mom.

Have you considered speaking with APS. How many siblings are you altogether? Are you together in watching this, keeping a diary, and etc? This may become an adult protective case.

Call adult protective services and tell them there is a vulnerable adult who needs a visit.

Just say " we are taking Mom out to eat " and then dont bring her back until you have a clearer picture of what is going on and bring her to a Doctor for a Diagnosis . There Isn't Much he can do even if he calls the Police . Make sure she is safe and then get Healthcare proxy . Sounds Like It is Not a safe Place for her .

Have you contacted APS?

Wow…so sad.

I agree with Southernwaver, do whatever you can to keep your mom safe.

I would be very concerned about your mom’s situation.

If your suspicions are correct about drugs being involved, then this situation will become worse.

I grew up with an addict. Unfortunately, my brother was an opioid addict. Anything of value had to be hidden or my brother would take it to sell for drugs.

Best wishes to you and your mom.

Listen to AlvaDeer!

Call adult protective service in your area and ask them to make a wellness visit

How is he 'still' stealing narcotics from family? If it's happened more than once, some of the blame is on the people getting meds stolen. If he's stealing other people's meds, he has a problem. Why in the world is any of the family still allowing him access to where the meds are stored? That part of the problem needs to be fixed by all of you in the family - if he's around, put your meds in a secure place. Do not store Rx meds in the bathroom.

If mom has memory issues, it's going to be hard to figure out where all the issues come from inside the home. She may not want a haircut. She might be the one paranoid about leaving the house and says she needs his approval. On the other hand, he could be the control freak. You can 'suspect' he's using money for drugs, but you really need to have some proof. Have any bills gone unpaid that they used to be able to cover? Asking kids to pay for things that they used to afford?

Address his drug problem first: Can he care for her while taking whatever it is he takes? Does he have a criminal record for the drug use...probation...etc. If so, children need to get an elder attorney involved to take control of the bank accounts to prevent the money being used for drugs. You may have to get adult protective involved to go in and talk to them separately and see what they think.

It might be time for kid(s) to spend about a week with them. Come up with a reason - visit from an out of town child??? Maybe one of you having some work done at home and need to be out of the house for a week? Observation and a little snooping will be the only way to find out what's going on there.

My dad's wife was MPOA and refuses to tell us anything about his medical condition (dad has mild dementia). I ask him when his dr. appts. are, ask him to confirm it with his wife while I am there (we look on their calendar) and then I go to his appts with him. I have given a copy of the HIPPA form to his drs so I can call to confirm the appointments (sometimes she changes them). After SEVERAL years of us kids talking to him, we were finally able to get him to change the MPOA and POA to us kids. However, MPOA isn't in effect until he is declared incompetent which will happen with his next cognitive test next summer.
See if you or one of your siblings can go to the medical appointments with her. Keep a list of all her medications and/or get the list from the pharmacy. See if you or someone that can stand toe to toe with your step-father can get on their accounts to see what the situation is. Also, as recommended below, keep a journal of every interaction. It will help jog your memory should you seek legal help.