Just a buffet in Galleries First these days sadly. There is drinks ordering via a basic app/web interface. BA fly to DUB (technically a domestic flight as it's within common travel area) from T5. If you wanted to fly EI that would be from T4. EI is a partner airline to BA but not a Oneworld member. There's an overcomplicated rule book about who gets access to lounges in that context - I think BA codeshare with BA Gold (but not any other oneworld airline equivalent status or BA silver) gets into LHR EI lounge, and no guests. So in summary you're probably better off with BA (so guests allowed into lounge) and having either lounge buffet or buy food in terminal)