As far as the first situation is concearned, the predalien would definitely have the element of surprise, but after taking out 1 or 2 of the preds, the others would catch onto the situation & hunt the creature down inside their ship, & would eventually find & kill it.
The second situation is completely farfetched though, 70,000 xenomorphs would absolutely obliterate the predators without question. In Aliens, there were nowhere near that amount, approximately 157 colonists were taken as hosts, according to Ripley, which equals the same number of aliens. 157 is still far too many for 7 predators to fight off by themselves, so they would be easy pickings in this situation.