what is the definition of Ahl ul Bayt

i wonder y we are not discussing three other daughters of prophet

Hazrat Zainab
Hazrat Ruqqiya
Hazrat Umme Kulsoom

does the incident of Mubbahla was the only yardstick to identify the ahle bait ?
what about the daughters of prophet who had died before dat incident ........ shud we ignore them.

my question to those who says that there are only 5 ahle bait

further if there is hazrat ali then why not hazrat usman ( if becoming son in law is the criterion)

if there is hazrat ali then why not hazrat abdullah bin abbas (( if becoming cousin is the criterion, )