(This is not accurate, I'm just doing what I think their ideal traits are)
𝙻𝚘𝚞𝚒𝚜: I think the kind of person Louis would normally go for would be someone confident and or charismatic. He would probably like it a lot if you laughed at his jokes, even if they aren't funny, and if you just seem to enjoy life even when it is crappy.
𝙼𝚊𝚛𝚕𝚘𝚗: I think Marlon would like someone who was motherly and caring, because he carry's a lot of stress on his shoulders as the leader and would need some kind of comfort. He would also probably like it if they were very hardworking and dedicated, because he ain't a lazy person.
𝙼𝚒𝚝𝚌𝚑: I think Mitch would like someone who was calm and cool-headed (which is pretty much the opposite of him) because, if he ever gets out of control you can be there to help him get through it. The person also should be very loving because I feel as though Mitch doesn't get much love, apart from willy. (I kinda also get a feeling he would be into shy girls, but I don't think that would matter)
𝙰𝚊𝚜𝚒𝚖: I think aasim would like someone who was smart and used their brain wisely. He would probably also like someone a bit on the quieter side, because aasim needs his space sometimes and you would need to respect that.