My husband's father was 96 when he married his girlfriend of many years, who became his fourth wife. They married without telling my husband or his two sisters.
The father had originally set up a trust to split his estate three equal ways between his children. No house involved because the dad had sold it years previously when he and his girlfriend moved to separate apartments in an assisted living facility. The father told my husband that the many gold coins which were stashed in a safety deposit box (my husband was on the signature card) would no longer be left to him, but to the new wife.
Well, when the dad died, the wife not only wore one of the gold coins made into a necklace to the funeral, but also announced to my husband and his sisters that the trust had been eliminated from the new will AND everything divided between the sisters and the wife equally, with my husband given a nominal $10,000. bequest.
What a witch. By destroying the trust, more of the multi million dollar estate went to taxes. Eventually, one sister gifted my husband over several years a portion of what she had received to make up for the change in the will.
My husband had flown to Florida to get legal counsel when the marriage took place regarding competency of his 96 year old father who had resisted marrying this girl friend for years. He found out that basically if you can zip your pants, you're competent in Florida. The wife found out from the other sister --the one who didn't share--and that's when she became determined to have the will and trust changed.
Good luck. Your husband 's father has undoubtedly been worn down over the years by this wife. She will likely get what she wants. Better resign yourself to it.