Ok guys couple of options
we check out the basement and send the kids to the 3rd floor either alone or split the group (we probably all know the saying about splitting up the group)
we all go to the basement or to the 3rd floor
If there is something trapped in the basement we should make sure it's secured until the children and any others are safe.
(depending on your level of paranoia one might think someone is trying to lure us to the 3rd floor and keep us away from the basement.......to what end, time will tell, perhaps the creature is the ill woman......)
How did this creature end up in the basement or get into the house? We should approach and listen for any commotion.