Okay, so I know this is kind of a messed up thing to ask (haha) but how high are the restrictions on breeding related pets? What i mean is, I know a parent can't breed with its offspring, and pets can't mate with their siblings or half-siblings, but what about two pets with different parents yet a same grandparent?? or same situation except great-grandparent?? I don't really have any pets to test this with but if anyone knows i would appreciate some info on this

So long as it isn't brother-sister (pets share same parent, either mom or dad) or parent-offspring (son/daughter tries to breed with mom/dad), it will NOT work.

Otherwise, everything under the sun besides the above works.
You can breed nieces to uncles, nephews to aunts, grandchildren to grandparents, etc. Cousins to cousins work as well, which is cost efficient when using essences.