My brother in-law has been put into a memory care home and his wife is spending money like crazy on junk. What can we do to take care of him?

Sounds like you need a lawyer to file for guardianship. Just because you file doesn't mean you will be awarded guardianship.
It could be said that your brother made his decision when he married his wife and made your husband second. I know this is stressful.

I’m not sure what your husband’s healthcare has to do with his brother’s  wife or his situation. Could you clarify? And, after whose wife? Are you writing about his sister-in-law?

If I decipher your post correctly, you are concerned about your husband’s brother’s wife who is spending money. I can say that if you or your husband don’t have a Power of Attorney or Guardianship, or if your names are not on his bank accounts, there isnt much you can do. Anyone else have an answer?