I understand your pain... United gives 24 buddy pass segments, and extended family (grandparents/grandchildren, parents in law, siblings) can get a slightly lower rate and slightly higher priority (higher than normal buddy passes). There is also the option to exchange the buddy pass segments (while keeping extended family ones) for a second person equivalent to a spouse. I think that may be the way to go.

Oh, just to give you an idea of how much buddy passes cost: Our agreement with a few carriers allows for accompanied companions, generally at ZED high. I looked up one nonstop route shared by United and another airline, and for an employee+companion's taxes and fees, the final cost is actually slightly cheaper for me to go on that interline route, and it's unlimited compared to buddy passes.