Depending on what their exact skills are, you might consider training them in Pressure(PG) or 1-on-1(F). Since they're only 5 pot players, what will make them useful down the road (and what will help you sell them for plenty when your team outgrows 5 pot bigs) is being well-rounded.
And when it comes down to training big skills, what I suggest is to make use of the elastic effect while trying to avoid the "imbalance penalty." So do something like train IS to ID+3, Train ID to IS, Train RB to ID/IS, repeat.
You might be interested in the training simulator:
(229484.1). It will let you play around with different training regimen, get a sense of where your players will cap and see what kind of training you need to do to build the players you want to have.