Firstly, you may disregard parts or the entirety of my advice or criticism. I'm not the best by far, but I still have help to offer. With that said, I would like to divide my suggestions into two parts: 1) player (generic tactics) and 2) map specific.
1)
A. Probably what is going to have the most argument against: all 5v5 players should be assault and preferably Voss/Krylov. In some cases the commander can be recon to set rdx/mines on a flag, but I would still recommend all assault. We can have a discussion about this, but I have never seen a team consistently win without all guys running assault.
B. Always practice with TWL rules. I think someone from EG said your team planted an IDS. Some teams would force you to forfeit for using an illegal item, so your team should get used to not having them. Besides, the commander should be pointing out people often enough to make IDSes obsolete.
C. Keep close, but not too close to each other. You don't want a lucky grenade or rockets to take 2-3 of you out. I don't think you guys had too much of a problem with this; I think it was more you were backed into a corner (had one flag left) and had to face us 1v2-3 as you spawned in.
D. Use rockets more. Some people say they are ubber cheap and they probably are, but they are still a part of the game and very effective for killing, hurting, slowing down a player/group, defending flags and choke points, etc. They can be easily avoided, too. Keep moving; try not to hide behind obstacles, but if you do, put 3-5 "feet" between you and the box you're behind so the rockets cause no or little damage. Never just duck and think you're safe.
I'm heading out soon, so I'll have to finish this later. Just wanted to give you all a debrief while you still had the matches fresh in your mind. I'll watch the BRs in the next couple of days and give further suggestions as well as begin talking about maps. I'll probably do: Tunis, verdun, gib, berlin, sidi then the rest unless if you want certain ones before others. Also, if you want this confidential, you can put it in your members' only section and PM me the responses.