Until and unless you confirm the list of legal heirs even though there is a Will bequeathing the property, it is not advisable to venture into the purchase of this property.
If they claim ownership through Will, ask them to first get the property mutated to their respective names as per the contents of the Will.
Once the Will is enforced, it will be evident that they have clear and marketable title to the property, after which you can obtain a legal opinion from an experienced local lawyer and proceed with the proposed purchase if recommended.