Divorce agreement and last will/ trust contradiction

Location: Illinois

My parents have been divorced for about 20 years, yet continued jointly owning a rental property. Their divorce agreement stipulates the rental property should be held in equal interests in their respective living trusts. Each living trust should incorporate a special needs trust to even fit my disabled sister. They also had to review and agree with the others trusts.

Since then my dad has received awful advice and seems more focused on control vs benefiting my sister. He plans to leave all his money to my cousin, whom I believe is making false promises about taking care of my sister. He does not want to use a special needs trust and has stopped talking to me. He updated his last will and trust about a year ago but did not show my mom the recent update.

Would a 20 year old divorce agreement take precedence over a recent last will and trust?