I just come across these two words used to describe "home rental". However, I want to know the difference between these two words and whether they can be used interchangeably.
My understanding is that
家賃 can be used to refer to:
借家 refers to the house being rented.
Simply, No.
Your understanding is correct except that 家賃 does not mean "to let" (only your #2), thus not interchangeable.
If you are confused, may be this way of thinking helps you a lot.
Chinese origin Kanji, when divided, the former is always (not entirely) adjective or verb. (This becomes sometimes different for JAPANESE KANJI because JAPANESE KANJI is not actually, KANJI.)
家賃 ⇒ 家(house's) / 賃 (money/rent) ⇒ the house rent.
借家 ⇒ 借(rent (v. tr.)) / 家 (house) ⇒ a house rented.
Have a good night.
