Jam Laeng Rak (2023)

Both female leads...
fake their identities,
have to live in a family's house,
fall in love with one of the family members,
the other family member made them fake it,
have one younger brother,
are poor...

Other stuff is pretty similar too

Female lead pretending to be someone else and Male Lead trying to prove that she is a fake. Both male lead and female lead are nice...