Time paradox - Thanos

A lot of plot in end game focuses on not screwing up the timeline in gathering the infinity stones in the past. Our heroes do pretty well in this regard.

BUT

There is a major problem. Thantos and his army come from the past and they are turned to dust by Iron Man. If Thantos and his buddies from the past are dead how can the events of infinity war and other major mcu events occur?

Even if you hand wave this away by saying stark did kill them just sent them back to the past and wiped thier memories there is another problem. Both past versions of gamora and nebula are in the future so can't take part in events they took part in.

My head hurts.

Am I missing something?