Wow, that's a lot of rent.
Ok, so, lets do the math
20 checks x $50 discount given means that they are giving you a $1000 discount every month.
Normal rate would be 20 x $800 = $16000 / 8 apartments = $2000 per apartment.
You don't have use of 2 apartments. $2000 x2 = $4000
THAT's how much of a discount you should be getting every month, which comes out to everyone paying only $600.00 each month ($16000-$4000 = $12000 / 20).
You said this has been going on since September? In my opinion, you have have been overcharged 5 months (Sept, Oct, Nov, Dec, Jan) x $3000 ($4000 that you should have been discounted - $1000 that you were actually discounted) = $15000
Since rent for the month is $16000, if they are offering ALL of you February for free, that is a fair trade, from a strictly financial position. Even slightly in your favor. If they are only offering SOME of you February for free (which is what it sounds like they are offering), that's bull, and you need to sit down with them with a calculator and these numbers.
If you now have the use of apartment #7 (I couldn't tell for sure), then that would adjust slightly, they might have
only overcharged you $13000.
From what it sounds like, they are offering you $2250-$2400 off (3 of you x either $750 or $800). How long are you planning to stay there? I might agree to that, if they agreed to lower everyone's rent for the next year to $700 each and got the people out immediately. If you aren't going to be there for a year, though, they need to give you substantially more than 1 month's rent free for 3 of you. That is a ridiculous offer and an unacceptable situation.
(Anyone want to check my math?)