Let's say you cast the find familiar spell, and summon a bat as your familiar. Obviously, a bat only has an Intelligence of 2, and can't communicate with you easily by any method other than your telepathic connection. Say I want to ask some bats in a cave if they've seen anything, but no one has Speak With Animals. Can my bat familiar communicate with the bats, and relay the information back to me, or would it be unable to do so, because it is actually a familiar in bat form? Would it have to change form to speak to other animals, or would there be one kind of "Beast Speech" that all animals would understand, considering that "Speak With Animals" works on all beasts?
In addition, say my DM let me have a Tressym as a familiar, a beast with an intelligence of 11 that can understand, but not speak, Common. Can it remember conversations, provided they are in common or being spoken by beasts, and relay them back to me since it has a much higher Intelligence than regular beasts?