Listen, Nothing have been said about the mother or mothers of both Madara and Hashi.
1. Madara and Hashi were not twins.
2. We do not know if they came from the same woman.
3. Madara mother could have been from the Hyuga Clan
4. Hashi mother could have been from the Uzamaki Clan.
Just saying, but anything is possible and in due time we will find out
We do not know much but I do believe that Uzamaki is a stronger clan than what we think and the SO6P could have well been the original Uzamaki and just look at Naruto carefully, he is a spitting image of the SO6P and if that does turn out to be true about the SO6P being the original Uzamaki then the Uchiha fanboys will drop dead.