Aunty died and it came to light that her will was changed by her sister and nephew a year before. What can the family do?

If the will is in probate it's now public record. Call probate and make sure of the executor. Also explain that will was changed while Aunt was considered incognitant. Lawyer had to make the change. If your in the will, you must be notified by letter and as executor she has to follow the will if not u can sue.

Having dementia is not a disqualifier for enacting or changing a will. As long as they understand that one specific thing they are agreeing to.

Well. You can ask to see the will. Have you tried that?

The Will is valid if your Aunt was able to understand the contents of the Will and was able to make changes. Only your Aunt can remove your sister's name as Executor, and only your Aunt can assign her sibling to now be the new Executor.

If your Aunt had dementia during the Will changes, only the Attorney can stop the changes if he/she felt your Aunt was not of clear mind. Some people with dementia can have clear time frames during the day.

Only your aunty could change her own will. The legal question is whether she was competent to do that at the time it was changed.

Unless she was extremely wealthy, it is likely that there wasn't much left after 10 years of dementia care.

Was she on Medicaid, do you know?