What kind of pass do you have? Interrail does not have group passes as far as I know.
If you mean an #DiscoverEU pass, than you get an Interrail when you choose Flex. This means everyone gets an Interrail Mobile Pass - Global Pass 7 in 1 month. Everyone has a Ticket and you don’t have to go together.
Fixed Option, you have to use it with your friends. Because you get standard tickets from #DiscoverEU.
For more information about #DiscoverEU please ask directly via DiscoverEU | European Youth Portal (europa.eu) or the information you get via mail.