That depends on how the trust was established and what the terms are. If Granddad was wise and established a supplemental needs trust for the kid, then the assets will be protected. But if the distribution plan was done as usual, the assets will be available.
How long to probate a will?
The process can start immediately. It may be weeks or months before a distribution from a probate estate.
What if jointly held?
The joint account assets can be distributed almost immediately. Per stirpes means that if one of your kids has dies, that deceased kid's share goes to their kids.
Time to consult with a local elder law attorney with a probate practice because it's too late for the power of attorney, you'll have to go for a guardianship or conservatorship now... Lesson: Don't wait until it is too late
Consult with a local elder law attorney... generally payments made to family members will be treated as divestments and create a penalty period. Do not "guess" about this stuff, the consequences can be... severe!
It might be valid, but gosh, it sure does stink, doesn't it?
The question is whether there was "undue influence" and given the circumstances you describe, it seems to me that the burden of proof, proving that there was NO undue influence, would shift to the caregiver... You need to speak with an elder law attorney with experience in probate litigation asap!