Legal Question in Wills and Trusts in Pennsylvania

No. It will depend on when she added you and her mental condition at the time. If she was early on in the Alzhemer's phase, she may have been perferctly competentto add you. If you are concerned about this, then I suggest pershaps speaking to her doctor (if you have a healthcare power of attorney). If your aunt does not have a financial and healthcare power of attorney, then she needs these documments provided that she is mentally competent to execute these documents at this time. If she is no longer competent, then you or someone else will have to seek out guardianship for her.

Your cousins cannot contest the addition of you to the bank account for any reason - they have to have grounds and generally will have to assert either lack of mental capacity (which can only be established through medical testimony of your aunt's doctors) or fraud of some kind or undue influence. If they cannot establish any of these things, then a challenge will go nowhere. However, your aunt could live for many more years and there will be a timeframe to bring any challenges while your aunt is still alive. Moreover, neither I nor any other attorney can predict how much money your aunt is going to have in her checking account at some date in the future when she passes. The reality is that at some point, your aunt is probably going to have to be institutionalized in an assisted living facility or she will need some kind of private care. I don't know what assets your aunt has or how she intends to pay for such care if she needs it. It may be that there will be no money left at all.

Your aunt, if she is still competent, should speak to an elder care attorney and make sure that she has planned for circumstances before her mind goes altogether. Just making a will may not be enough.