The present civil action filed by Amarin in Delaware is a standard patent infringement suit without H-W overtones. You correctly observe that H et al have the opportunity to plead non infringement as well as patent(s) invalidity. You may want to rethink the idea of a 2nd H-W suit being filed before R-I patents with CVD indication coverage expire in the 2030s.
Perhaps I do not understand your position as you present it.
Hikma cannot challenge R-IT patents before ANDA exclusivity ends this Dec, then there's a 30 month stay before FDA will accept an ANDA challenging R-IT patents. All Hikma can argue is whether they are infringing R-IT patents or not, cannot argue the patents are invalid - to do otherwise would allow them to bypass that 30 month hurdle.