That's a totally different situation and involves a debt of the deceased, which would normally be paid out of the estate before distribution. Other than the two grounds mentioned (duress/incapacity and equitable grounds), what other grounds are you aware of where a non-spouse/child can challenge a will? One can never know all the circs of any of these posts, but can certainly give a reasonable, educated, opinion based on the facts as given.
As with all posts to this site, advice/opinion here is not a substitute for professional advice and no-one is suggesting it is. However, the reason that this site is helpful is because its members give *some* information/share their knowledge about certain topics. If you have reasons for thinking that anything said on this thread was incorrect, then fire ahead, but I think that OP will probably find the opinions given helpful rather than us all asking him/her about all possible permutations and combinations and guessing at facts not mentioned.
Sprite