forgetting about the plecs, and tank size, you don't need to get a matching molly as there is no certain way of knowing who they bred with, and most mollies come pregnant and can store sperm for a long time (aprrox. 8 months) so unless you make sure she isn't haveing any babies (by waiting a couple of months) and then putting the matching couple in a separate tank, you probably won't have to go through the trouble of buyng a pair. Although, with an orange moly another orange molly would be best.
well i dont think if i get a small male molly that it will go for the big ones it for my small mollys and my plecos have stayed a certain size to the same size as me tank
If you want a matching couple always go with the same color, or else it wouldn't really be matching. Trust me, mollys will breed with everything from plants to fish 3 times their size, my guppy males prefer bigger females and don't like the ones that are about their size. And once again, your female is probably already pregnant as they store sperm. The plecs are probably stunted, this happens when a fish is in a smaller tank that they should be in. Their organs grow, but their body doesn't because of the tank size, they live a short and painful life. Unless you have a 100 or so gallon tank you would need to rehome them as soon as you can.
The organs-continue-to-grow thing is actually a myth (apparently anyway) but forced stunting is certainly cruel. Your plecos should all be rehomed immediately. Though, in fact, if you are doing your water changes regularly enough, there shouldn't be any stunting (which means the fish are going to grow far too big for your tank or for you to find new homes for in no time). If they are indeed stunted, you are not maintaining your tank properly and need to increase the frequency with which you do water changes. Also, plecos are territorial and will eventually start to fight as they become more crowded. It's simple enough to return these fish to your local fish store and save yourself some time (and money) in advance.
once again, if you want to match by color, it's always best to get the same color, so if you have orange, get another orange, though I wouldn't add anything else as the tank is probably very overstocked. And I have to ask, again, what size is your tank?