You can breed son to mother if you are just planning on eating them. Despite what some folks would have you believe you are not going to end up with three legged, two headed piglets due to inbreeding!
When you breed tight like this you have the chance of combining all the really good genetics & producing superb piglets, You also run the risk of all the bad genetics coming together especially if the mother is not that good to begin with. When breeding tight like this & selling for breeding stock you need to really cull hard, only selling the best for breeding & the rest as feeders.