They are not latecomers. That's what you're missing. They had no intent to come. There was no arriving. What happened, in a more technical sense, is you left the battle that your party was in. You started your own battle with an add in a 2nd location and then dragged your battle on top of the previous battle.
If I say me and 3 people are going to a 4v4 shootout against T people on X street.
That is our fight, that is our shootout. The 8 of us.
If you, as a member of the group, go to Y street, and start shooting at Z people, and they shoot back, and you run away.
Just because you came to X street when you were getting chased, doesn't mean that Z people are arriving/participating in the original shootout. I ain't got nothing to do with Z people. I came to shoot T people, not Z. I'm not shooting Z people, and they're not shooting me by default. If I see bullets flying, I'm ducking and letting you die, I'm not saving you because you wanted to run into a 1v3 shootout I didn't sign up for. That's not my fight, that's not my battle. Now if another person in the group decides they want to take a higher risk of dying that day, cool, that's their life, they can shoot Z people. And when Z shoots back, both of ya'll are gonna die. And I'm gonna hop a fence with the last homie, and then I'll tell ya mom's that you went to go shoot at some people without us and got killed in the process of them chasing you, and I dipped because we were getting swarmed out. And we will look up on the news, they gone talk about how you had good grades in school, how you played sports, and they gonna make a t-shirt and have some nice candles for your funeral. But noone is going to blame me for your death expecting me to take bullets from a random beef you started.
When you went and shot at those other people, you are no longer my ally, you are not part of my party. You have acted on your own, outside of the group, you are not entitled to benefits of being in the group. You handle your own business.