Also relevant: Idk if you are doing heroics then I assume you are actually recruiting quality players and the like. If you know they are extremely skilled, funnel gear into them once you know they won't just hop servers or to another guild once you gear them completely (unless ofc you are #1 on server or highly ranked in world).
The best way is really swapping people around dependent on loot needs whilst ensuring you have the group to kill the bosses, it can be a pita swapping people after every encounter, but so long as no one wanders off or you have a lock to summon and make the people you have to boot use their teleporty faction base thing so you can get the new folk zoned in it saves a lot of time.
Apart from that, it really depends on the gear level difference I guess, if you have enough alts within the guild it may be worth setting up normal runs for instance to acquire the last few normal BiS items, like trinks and weps just so that they can have everything upgraded via VP when they hit up the hcs. Oh yeah, make sure you spam Hc Scens to cap the VP if you're not already, you cannot always rely on people to do it themselves I find.
personally, i'd run the raids concurrently, unless you actually NEED these people to fill the main raid, in which case... thats an entirely different problem... and the goals of the main raid may need to be adjusted while your raid group matures.
My guild gear boosted a returning player from 505 ilvl to 526 in one night (hunter, got 4set heroic and hc wep among other things) he got to do everything but Lei Shen and Ra Den.
As long as the recruit knows how to play and how to do the encounters it doesn't matter as long as you have main raiders with enough gear to compensate, this week I think we had 6-8 trials for 11heroic bosses without too much wiping.
We raid 25man though, going to be considerably harder in 10man I suppose.
We took someone with a 488 item level to heroic Jin'rokh and got it down. That said, if you're aiming for heroic modes you may still have to clear normal once or twice to gear them up before bringing them into the harder bosses. You won't be able to walk around with a 490 or 500 on some of the fights.
Depends if its 10 or 25, if it's 10 you'll prolly have to gear him up more, if its 25... meh you can easily carry an under geared player you should still clear 11/13H ezpz.