1. The property can be purchased even if one of the co-owners is deed and Will is nor probated.
2. in that event you have to make all the legal heirs of the deceased co-owners including the nephew party to the deed.If they join as confirming party, that will also do
3. if all of then join in the deed of sale then you can safely proceed to buy this property. Once they join as conforming party then in future they can not raise any dispute.