What are the chances of pregnancy after sex with panties on but they're wet and he had boxers and sweat pants but the pre-cum may or may have not soaked through his pants while grinding?

Well its rare but there have been cases where a couple were both in their undergarments together, the man ejaculated and the sperm made their way through the moist panties and got the girl pregnant....

As long as you are in the early stages, you can do so as usual. In the later stages, switch to doggy. (Not to get too graphic)

No it is not possible to get pregnant while your both still clothed.

Yes..but it's less likely than if you had intercourse.

Less than normal; but if a pregnancy would be problematic, you should still not consider it absolutely safe; and rather use other contraceptive methods.