Is 5 yrs too long to initiate a dispute of a will and its bequeath.

My children's father died about 5 years ago and cancelled his life insurance right before dying and gave all of his 401K approx. $500K to a woman in Seattle WA who rarely came to Colorado, they rarely saw each other, and she never came to the hospital, called him, or attended the funeral. Of the three children, two are males and are his biological children. As their father, they are both bipolar and it has been very difficult to deal with them since he died. They are 31 and 37 yrs. old. Neither can hold a job and both are on the edge of disaster all the time.