https://seagullstickets.com/documents/pdf/1718/ST1718_FAQs.pdf
That said I see season ticket holders in the family stand all the time that never have kids with them. Not sure what that is all about.
Friends of mine have just moved into a block of 4 seats in the family stand as a result of exactly this. Think when moving out of the family stands in a big block you don't have much choice where you go but are at the top of the seat moves list.