I think what would be more disturbing would be his mum making out loudly in the next room without considering her child will hear it. That is so damn wrong in many ways.
What would be even worse from what I experienced in my life is hearing your neighbors making out. Also I found a funny thing about something like that a few years ago I was walking to work around 5 am hearing some people making out at their home with a window wide open on first floor. Very loud, I bet a lot of neighbors complained or fapped. But I found it to be quite funny if they didn't realize what they did.
That said, I think his mums BF shouldn't be sleeping on the couch there. Either get a room or a house.