I do not think the issues you detail would cause a deed to be invalid. Go see (and pay) an attorney if you would like more detailed analysis.

Why dont you go talk with a real estate or estate attorney and have them look up the deed...

If you have an inheritance in your name, then you need to talk with an elder law attorney about how to handle this so that you receive the most...

Perhaps you do not need an appeal. If the opposing is appointed and it has been longer than 6 months, then asking the court to order an accounting...

Power of attorney is revoked when the grantor of the power of attorney dies. So, your father-in-law and mother need estate plans. See an attorney.

Most probate lawyers have seen this issue......................................................................

If the heirs/beneficiaries agree then there should be no issue.................................................................

You need to talk with an elder attorney asap. You may have better options than spend down. To show a payment to you is not a gift from the mother...

Your marriage should have nothing to do with daughter's benefits..........................................

See an attorney. Perhaps you can open an estate for decedent and sue on her behalf for return of any funds improperly taken from the estate.