Stalling lawyer

My siblings and I are trying to settle my father's estate, however we are having issues with our step-mother.

My dad and step-mom were only married for 3 years so the only thing under community property is my father's truck. She was not included in the will nor was she listed as a beneficiary of his IRA accounts.

We came to a verbal agreement to pay her half the value of the truck plus user right fees. We had all the paperwork ready, but her lawyer wanted to list her assests as well on the paperwork along with our full listing. A month has now passed and her lawyer will not return our lawyer's phone calls to settle this. Is there some guideline or rule that prevents a lawyer from stalling this process? Other than pushing this to court, what else can be done in this situation where we have an agreement, but what seems to be lack of interest, is preventing us from closing this out?