Father Left Inheritance Tied Up In A House

Michigan - My father remarried in the 90s and put $100k into his new wife's home. My father typed up an agreement that his contribution would be reimbursed first when the house sold and the rest of the money from the sale would be divided between all the kids. This document wasn't ever signed outside of him typing his name and the date, but I do have this paper. My father died 20 yrs ago which was before the house went up for sale. At the time of his death, my step mother gave me a card saying she'd only reimburse $80k when she sold. I also still have this note. Well she recently sold the house without letting us know, and she is now not willing to reimburse any of what my father put into her house. Do I have any legal standing to go after this money that's supposed to be divided between me and my siblings?