When I run a whois on the offending ISP, it gives me a list of other contact names. should I forward the spam to them too?
No. The contacts shown on InterNIC are not for use by spam fighters. ISPs have abuse addresses for a reason. It does your case no good to spam the offending ISP by forwarding the spam to every known contact address. There are rare occasions of server security issues, DoS attacks, etc. that might merit communication with an ISP or server administrator.
