Bringing a new cat in a house where a kitten is!

I have had Carmelo(he is about 8 weeks or so) for about a month or so. My friend just moved in with me(temporary) and she has a cat, Vicious, also who is about a few months old. At first I didnt want her to bring her cat, but I decided to be nice. When they first met, they sniffed each other, pawed at each other's faces, and meowed. It looked like they were hugging for a while and then it was like they were wresting. We let them do that until I heard one of them meow real loud. A lil while later Vicious followed Carmelo in my room and they were wrestling/playing under my bed & then I heard a hiss and I broke them apart. I don't know what to...I know Carmelo is very aggressive in general but I dont want to have to listen for them fighting all the time. What can we do?

Random Info:

- they wont share litter boxes or food
- Vicious actually plays with toys, while Carmelo enjoys playing with my toliet paper, sneakers, robe strings, etc.
- Carmelo sleeps in the room with me & Vicious will be sleeping in any random spot in the house
- They're both indoor cats

I think they get OK, it is common whey they play-wrestle it is rather hard, one sometimes dont know if it is for real or play. Here it sounds like play, definitely.

Dont worry, be happy.

Sounds normal to me. They're getting along just fine. They're not fighting at all.