Losing my mind..

So my fiancé lives with me and my 5 year old son and every other week he has custody of his 6 year old son. He picked him up Friday afternoon and the kids have been fighting over games and toys, making messes and just screaming and yelling. My fiancé hasn’t spent any time with his son this weekend and I have had to deal with the kids arguing and being wild. Currently he is taking a nap while the kids are running wild and I just can’t take it. I understand he is tired from working so much but I feel like he needs to just suck it up and spend time with his son and help me with the attitudes and the mess. He is a very good dad and I don’t want to complain, but this weekend had been nothing but a headache so far..