I'm not sure I understand what you're asking because you didn't give us enough info.
What is the actual content of all those tracks? Are they individual tracks for different instruments, or different audience mics?
My general opinion: if the mp3 files are of a high enough bitrate (i.e. if they are transparent and don't show any obvious compression artefacts), and the CONTENT of the files is a superior recording, rely on them instead of less-than-ideal wav recordings. Obviously the ideal would be to have the best recording in a lossless format, but sometimes you don't have that.
But anyway, to answer the question very generally: just add the mp3 and wav tracks to SoundForge and mix them as normal, and then export it to a lossless format. For pure quality, you want to avoid an extra encoding step there at the end. There IS an etiquette question around this (i.e. you shouldn't be converting lossy files to lossless and then trading them as if they were lossless), but when we are dealing with a master tape you're creating, just do whatever sounds best and keep notes.