Frankly, I think it is a violation of the rules professional of conduct for attorneys to take a "will busting" on a contigency. I am not 100% on this issue, as it has never come up (for me) in 35 years.
I also think there is a distinct chance that if an atty did , s/he might violate rule 1.5 ( excessive fees).
I will have to research this one.
Are you asking because you do not think that the heirs would share as if there was no will?
In addition, unless he was not of sound mind or coerced, there might not be a basis for will busting.
He may have not understood what would happen if he didn't changethe will after you mother passed.
He may have meant ALL heirs. You stated that the "others" believe he accidently left out one nephew. Since he didn't mention him at all, that might be something to hang a hat on.
Did the atty you consulted mention anything about accidently leaving out one nephew, did you bring that up?
I will have to take a look at ND case law ( that shouldn't take long : ) , just kdding, small state pop. ya know; less case law)


