
I may be late, but what happend if they knot? They become mate right? But didn’t they knot it already?

I cant answer this with a 100% certainty but a knot in the animal kingdom is used by males to assure that their "seed" is planted or what not usually they dont get small or go away untill they literally cant cum no more. And yes they have knot before and it doesn't change their relationship it just feels painful for the receiver since after a knot is made it cant be taken out and if tried its painful. Hopefully this makes sense.

The knot in the omegaverse is something that belongs to the alphas. It'll block their penis inside the omega to make sure that the omega will be fertilized.
And, if an alpha and an omega want to be mate the alpha has to bite the neck of the omega.
But, you know, omegaverse is one those AU that can be change. Even if there're "rules" everyone can make it their ways. So who knows. But for now I guess the knot in this story is the definition i gave you above.
Another masterpiece ლ(´ڡ`ლ)