If you're in F or J it's a moot point as each pax in those cabins has entry. If you're in Y you can bring one guest only. Pay for entry policy is per the lounge you choose and often down to the location you are at.
Traditionally the Lounge Matrons are a hard nut to crack and the forums are littered with many similar stories about Atillaress the Hun door guards.
Best bet is to get chatty with another single travelling *G at check-in lines and see if they'll coat tail one of your trio into the lounge with them. This option has a fairly good success rate in my experiences, but there are those who of course won't and can take offence at being approached.