Unlike Telegram, Signal is end-to-end encrypted, which means that Signal themselves cannot read your messages, and therefore could not be compelled to divulge them. Because of forward secrecy, even if recordings of an encrypted exchange are made (and as far as I can tell Signal does not record them), they cannot be later decrypted with a compromised key.
Yes. Signal has perfect forward secrecy. There's no way any government could compel them to release private chat information: they are literally unable to do so.
Even so, a government could still block them until they realized it's futile (or something). The end effect is in their favor: users to move to other platforms that are not as secure.
WhatsApp does/might (who knows, they are not transparent about it and it is closed source) employ the same end-to-end encrypted protocol as Signal does (for some users):
