Welcome to the forum !!!
A windscreen leak would be pretty unusual. Most leaks are from behind the door cards (ie the internal plastic lining comes adrift - allowing water to run the back of the door card/insert, pool in the lower door seal & overflow onto the carpet). Maybe your winscreen has been replaced at some time & not properly sealed ???
As for the seat - have you inspected the wiring loom underneath the seat. Maybe a back seat passenger has stuck their foot under the front seat & accidentally loosened the wiring harness.... If not, then an auto electrician should be able to work out if the problem is motor or switch related - there usually pretty reliable.