Up to a party of 6 I had NEVER a problem to check in at:

UA: 1K (or if no 1K there, with national First or international business)
AC/LH/TG/RG/SK: StarAlliance Gold = business (if international first is wide open the take me there)
SR: business

Lounge:
UA: as Red Carpet member: Family members always welcome, even when not having the same name (mother in law, partner of my daughter) - only exception for me so far RCC in LHR were even I didn't get access after arrival.
When travelling international FirstClass (even after arrival and waiting for connections in the US) UA allows two non-travelling guests at their First Class Lounge (so in IAD, ORD and in Frankfurt).
StarAlliance lounges (with UA Red Carpet or 1K): guest-policy depends on the mood of the personnel (never a problem with AC in YVR, no problems with LH in Frankfurt & Duesseldorf but no guest access with LH in Munich).