My SIL took my Mom to the bank and Mom put her name on her bank acct. Can I ask for bank statement copies?

Your mom would have had to sign extensive paper work to give the SIL access to her accounts. This will not be easy to overcome nor can you force the banks to give you access unless your mom grants you POA or she becomes incompetent and you get legal guardianship.

You said there are 8 of us. Moms kids? How did the SIL get herself in this position of trust with mom and do you suspect she will steal from mom?

Goooood question. Why, suddenly, do you 8 children now want to know moms financial affairs? Was the trip to the bank just a random favor, OR has SIL always been there for mom, and NOW thatvmoney is involves, the blood offspring want to know? Not accusing, but it bears asking. There justvseems more to this scenario.

Where there's a sister-in-law, there's a brother. Your mom's son. Does he have power of attorney for mom? Unless someone other than your brother has financial power of attorney, you are out of luck. The bank absolutely will NOT share any information with you.

You can try to get guardianship of mom, but assuming her son and his wife are taking care of her, that's going to be hard to do.

How is it you happen to know mom did that? I would advise you to see an attorney.

Another point of information. Just because mom had a stroke does not mean that she is incompetent now nor before she had the stroke. IMO, it would be extremely difficult to prove mom was coerced in any way before her stroke. And that you're asking mom to see paperwork now, and she's saying no tells me she is thinking fairly clearly now.

It is not at all unusual for the elderly to gift their money to the people who are there for them in the twilight of their lives. Sometimes it happens because of purposeful manipulation. But that is not against the law.