How to challenge a will that is under suspision

Hi, My Father in law dies last month and we came to know a little after that from his eldest brother that he has kept a will behind. My FIL was a divorcee and was separated from my MIL for 30 years. My husband was in his mother's custody and only got in touch with his father 3 years ago in 2013. We were in great terms with my FIL since then. He has been a part of all social, emotional and financial events in our life. To our surprise on opening the will we found he had made the will in 2012(a year before he met my husband) and has given everything to my husband'd uncle. There are a lot of evidences against my husbands uncle which shows he has done some kind of fraudulent activities to come up with this outdated will. The solicitor is a great friend of my husbands uncle. My father in law had mentioned to several family members that he has amended his will in 2015 and my husband was made the nominee for the bank locker in which we found his property papers. We want to challenge the genuineness of the will. Please suggest.