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.
Beware of building up north allos will go through your walls and kill your animals specifically ur own allos after that they will target ur birds they have even spawned on the 2nd floor of my house I need to move back south
best way to take out a pack on foot is to go between the legs of one with a sword and keep slashing, usually try to stand under the alpha, it will not hit you with the bleed and since they are so large, they will actually hit eachother trying to get to you. once one is down, quickly run to the legs of another, rinse and repeat. took out a pack of 16 by myself in base flak armor while my buddy was walking our freshly tamed doedic back to base.
When encoutering make sure you don't get to close or they will come running at you they are very much like carnos but have bigger strides i couldn't out run a level 10 with 138% movement speed for me the best option is to RUN