Be the wiser character. If you think that all humans are an inferior threat to nature but you need their help, your character shouldn't be surprised when they verify your assumptions. You "knew" they were problems going in and you still chose to work with them, so seeing evidence of it shouldn't change your approach.
Someone calls you an idiot? You're almost 60, you've seen people like them get killed by their own foolishness, and you're going to become a god. Say something dismissive and move on. Young, rash adventurers get offended by casual insults. Old, wise sages know not to listen.
Unless everyone at the table wants to play a PvP campaign, just play the grumpy, dismissive old dude who puts up with the others because they're necessary to his plans. It's fun for the other players to bicker with a curmudgeon; it's probably not fun for them to get into a drawn-out PvP combat with someone you admit is too powerful.
So first, a couple of things I would do if you plan on doing something like this from scratch again in the future...
The first point I want to make is something I've learned from hard, bitter experience. Some players are incapable of separating inter-PC and inter-player conflict. It doesn't matter what their ages, experience or life skills are. This means you have to take this into account when you are planning on running a story that you anticipate will involve significant inter-PC conflict.
Also, where I am planning to run this kind of game, I always talk it over with players first. A little inter-PC conflict here and there is par for the course, but if I want it to play a bigger part then this conversation is essential. Some players simply don't like this style of play, or know that they find it difficult. Bringing it up at the start allows them to either back out gracefully or discuss possible compromises with you and the group. You can also get a lot of information about how your idea is going to work out simply by watching and listening to the way individual players react during this conversation. By the end of it you should have a good idea of whether your planned campaign is workable with this group of players, whether its a definite no-go, or whether you will need to make changes.
Now to cover your specific situation...
With this group, the first thing you need to do at the start of your next session is sit them down and outline your expectations. Players MUST be able to keep inter-character conflict in character. It is essential for the game to run smoothly for everyone's enjoyment. Don't try to lay any blame or point fingers here, just keep the discussion general and get all players agreement.
During play itself, if you or another player sense things are getting out of hand, then call a time-out. In character play immediately stops, no matter what the situation. Check whether there actually is a problem, as you might be misreading what is going on (something I've done on a number of occasions). If you still think there is an issue, take a break, allow people to get drinks etc, and talk individually to the players involved. Ask them why they were getting angry, what the problem was, and why they couldn't keep the conflict in character. Remind them of the agreement you made about this kind of thing, and if necessary bring those involved together to resolve anything outstanding away from the main group.
Assuming you've talked to the players directly involved and are happy with the responses, reconvene and carry on playing. However, this kind of thing may not resolve if players just find it hard to do this kind of roleplay without it seeping into inter-player conflict. If it happens regularly, then it will completely ruin the atmosphere in the group and rapidly lead to the breakdown of the campaign.
As a final note, given you've highlighted that a number of the players don't get on all that well out of game anyway, it's going to be a real challenge for you to keep any ill feeling from that coming into the game. It simply may not be possible depending on the players involved.
Best Answer
I'm going to go against the prevailing advice here:
If the other players won't let you play a character that you find interesting, because that character won't "pull its weight" in combat, they're violating Wheaton's Law.
If you want to play a character that is ineffective in combat but effective in other situations, that is your right as a player. You don't have to be part of every combat situation. Or every situation.
The exception is a character who is clearly and specifically against the party's best interests. If someone in an all-Jedi group wants to play a Sith, well, sorry.
I'm a DM/GM, so I handle this out of play, and I let people play the characters that they want to play. In the case of the explicitly antagonistic characters mentioned above, I'll steer the player towards a different character concept.