Need some clarification on s2s ssl

I am a bit confused about the s2s ssl and some clarification would be great.

I have Server1 which has some certificates installed already and I want it to have an SSL connection to my Server2. So to have SSL connection I need certs - i am a bit confused about the SSL guide…

If I get a CA signed cert - does it have to be the same CA that the Server1’s certificate belong to?

If I get a certificate generated do i import it to BOTH servers so it gets recognized?

When I started my openfire server2 I see 2 server certificates in there already - do i need to send them to the Server1?

thanks