Should we extract baby teeth molars, in a 7 year old, if the adult teeth are not present underneath?

Probably not. I would strongly advise that these teeth not be removed as long as they are not creating any problems. If there are no adult teeth to replace them, they will be very important as the child gets older to keep the all the teeth in the upper and lower arch in the correct place and position. So if they are not creating a problem for the child, please keep them in place.
Depends. If a primary molar is abscessed, it needs to be extracted. If there is no infection, then there is no need for extraction at age 7.
Only if a problem. Not if there isn't anything wrong with them.