Can I make a claim on the estate if we did caregiving for free initially?
If there was no agreement while they were alive that you and your wife would be compensated for taking care of your wife's parents, you cannot change the nature of your services as being done for pay as contrasted to being done gratuitously now. If their Wills were written while they were not of sufficient sound mind to make a Will or while they were under duress or undue influence from someone, the Wills may be found to be invalid. You should consult a lawyer and consider a challenge to the Wills. If the Wills are ruled by a court as to not be effective, their previous Wills, if any, will control. If they did not have previous Wills, the laws of intestacy will apply which would provide for payments to your wife.