Setup for multiple domains on same VPS

Hi

We have 20 domains into a VPS and have two IPs allocated.

How do we go with setting up DNS for each domain?

1) We already have one wordpress installed on http://www.sample.com . We can assign fixed IP to this domain from our VPS

2) Regarding other 19 domains, do I have to create A record on their domain mgt. and link it back to the fixed IP of the http://www.sample.com domain?

3) How do we do domain mapping after?

Please note all the 19 domains share same IP and http://www.sample.com has differnt fixed IP.