Here's my situation:
I always play with 2 to 4 of my friends in ranked or normal draft. Early game we all do well. We usually out cs, gank well, and have great map control. Late game (if we make it that far) we do very well and haven even staged several comebacks. However, it seems every game we lose is because of our mid game. We just seem to get caught out of position constantly, lose dragon, lose baron, get pushed, get backdoored, and generally start losing the game even with a great early game. Can anyone help us?

TL; DR: Great early game, great late game, HORRIBLE MID GAME. Pls Help.

Sounds like a common problem I have observed on my own and other teams. If you are winning during early game then the best thing for you is to keep farming til 20-25 minutes and then start team fighting, right? Well the problem is that lots of teams will force midgame early if they losing, which often results in exactly what you are talking about.
By forcing midgame I mean you are likely to face a 5 man push on one lane to try for a tower, which without the correct response, can easily snowball into a double kill bot, tower lost, and then dragon. That's at least 2k team gold. So just get used to winning early and quickly responding to a forced midgame so you don't lose your lead.

Unfortunately I don't play with very many decent players, only with randoms, so I can't offer much advice.

Do you ward?

Map vision is key to those out-of-position situations. Additionally, most losing teams will try to force an early mid game, gotta watch out for those. I'd recommend for the lanes to begin grouping together. Maybe top or the ad carry can stay to farm, but you guys should be getting together to work for objectives: towers, dragons, baron, etc.