Super Man wrote:

What kind of flea meds work great and are safe to use on cats

The reason they are coming from your basement is because they thrive in
humidity. As "buglady" suggested, you should use a dehumidifier.

A dehumidifier helps in more than one way. But most importantly, it
nukes fleas. Buy an inexpensive humidity meter (or two if you want
confirmation) and keep the humidity below 50%. Then fleas cannot
reproduce.

No chemicals. Also helps reduce mold. Probably helps in other ways
especially in a very humid basement.

If you cannot cut off fleas coming from the basement, you must
dehumidify that area too. The idea is to make sure no fleas can
reproduce and the only fleas that ever get on your cats are the few that
might make it into your home from outside. Any newcomers only last for a
maximum of three weeks, then they are gone.