I think you are going to have to look at cargo bikes. I don't know of any fat bikes with big enough spokes or a way to add any comfort for that second adult and that kind of weight.
Hi @Osman, that's an interesting question! It looks like @ReallyGoodEbikes mentioned Joulvert and they do indeed have a rear passenger seat thing going on. I haven't tested that one but it looks cool. I cannot think of any fat tire cargo models that were built for two, but maybe you could retrofit or modify a standard fat model, here are all of the fat models I have reviewed so far that you could explore: https://electricbikereview.com/category/fat/