I have not attempted to study three Romance languages simultaneously, but it might be easier to study them one at a time. Otherwise, you may risk mixing up vocabulary and grammar (plus it's difficult to memorize too many new things at once). It might be helpful to study one until you've finished an introductory textbook, and then you can proceed to practice your reading/writing etc. as you then pick up the second language and so on. With a little overlap, you avoid memorizing multiple conjugations all at once, and having committed, say, Latin grammar, to memory before you start French will make learning French grammar easier.
Horae quidem cedunt et dies et menses et anni, nec praeteritum tempus umquam revertitur nec quid sequatur sciri potest. Quod cuique temporis ad vivendum datur, eo debet esse contentus. --Cicero, De Senectute