Would definitely get rid of both lingard and Mata before Martial. Rashford isnt a long term wide player, martial is definitely more natural out there. Rashford is more of a forward playing out wide. He should be rotating or playing alongside Lukaku more (or martial doing that if rashford is back up left Winger). Imo, we dont really need #10's with how squad is shaped. Certainly not 2 who do a job on the right at best. So I would sooner bet rid of both lingard and Mata, get a proper right winger like Bailey, in and that be that.
I think the biggest problem with all this is how Mourinho sees his strikers. He never rotates them. Never subs them. Never moves them around or changes to go 2 up top. So lukaku plays almost every single game and the entire game, leaving no room for a back up striker. Rashford or martial or both would get loads of playing time if Mourinho had more flexibility in how he used his attack, but he doesnt, so there's only space for one.