When three or more allos meet up, the highest level becomes an alpha. He will be the one with orange glowing cloud on his back. Reducing the pack to only 2 dinos will remove alpha status from the highest level allo. This means it is usually easier to kill the weakest in the pack first and then the fight will be much easier. Multiple alphas can be created if a large group of allos form. However that are not invincible. Personally saw a group of 15 Wild allos with 5 of them being alphas get wrecked by a Lvl 80 giga. So even if you could somehow tame all 15, you would be far from invincible. A good step up from a carno, but they stand no chance against similarly leveled Rex or giga.