Found this in another thread:

-- COMPLIMENTARY ELIGIBILITY-----------------------
- GS/1K/ ECONOMY PLUS FOR FAMILY
- GS CUSTOMERS MAY HAVE UP TO 8 COMPANIONS OR PURCHASED
EXTRA SEATS IN THE SAME PNR IN THE ECONOMY PLUS AREA.
- THIS ALSO APPLIES TO UP TO 8 FAMILY MEMBERS/EXTRA
SEATS ON SEPARATE PNR EVEN IF GS IS UPGRADED TO UF/UB.
- 1K CUSTOMERS MAY HAVE UP TO 8 COMPANIONS OR PURCHASED
EXTRA SEATS IN THE SAME PNR IN THE ECONOMY PLUS
AREA. ALL COMPANIONS/FAMILY MEMBERS/EXTRA SEATS
MUST BE IN THE SAME PNR AS THE 1K MEMBER.
- TOTAL SEATS IN THE ECONOMY PLUS AREA SHOULD NOT
EXCEED A TOTAL OF 9.
- 1P/2P/3P MEMBER AND ONE COMPANION OR PURCHASED
EXTRA SEAT. MEMBER MUST CREDIT FLIGHT MILES TO UA
TO OBTAIN ECONOMY PLUS SEATING.