Why do you put such a big importance on the cultures of the factions ?
This is a question that doesn't need to be asked.
I would underline their strengths and a bit of their weaknesses, especially for a multiplayer-game.
(an offensive faction having more tough talk when you click on them, scars and powerfull symbols,
Except that their cultures are radically different from that. Bahaar are one of the two offensive factions. They are strictly regimented and very stoic. Their comments are quick, direct and to the point. ("Orders, sir?", "Yes, sir.", "Taking fire, sir!") They also do not say anything most of the time they are selected. They're also furry, so if they were scarred you probably wouldn't know. They don't use any symbols or markings, because for them these are to symbolise which house they are under the direct command of, and in this case they are not under direct command. Andhieli are the other, and they're the polar opposite. They're juvenile, excitable, undisciplined, eager and trigger-happy. (VERY trigger-happy. Expect them to shoot a lot of nothing they're supposed to.) They move around a lot, even when idle, and often detour or deviate from your expressed commands. They're also snide and disrespectful. ("Oh, no, I wasn't busy or anything.", "Alright, not like I've got much to live for anyway." "Hey! If you're not too busy connecting with your tac officer, we could use some help!")
a more defensive faction having all carrying their symbol of the hospital(have it being a red cross to make the player understand it faster)more whispering and talk about planning)
I'd rather not do something that will make the players assume the setting's primary antagonists to be the good guys. I'd also rather not associate the red cross with anything the simini do. Further, simini are arrogant, snobbish, xenophobic and conceited. Rather than whispering, they speak loudly and clearly. Rather than talking about planning, they dismiss their opponents. ("And you need, sir?", "Let's see what those stupid monkeys think of this!", "That better not have left a dent, monkey!") Their nobles are more polite, but are also much more arrogant. ("What is it you require of me?", "They shall not be able to stop us.", "Oh my, they seem to have chipped the paint.")