It's simple enough to get them on the database. Go to Seagulls - FC Online and register. It's very easy. Then add yourself to their friends and family, then you can buy a ticket for them.
Of course, you can also let them register themselves and buy their own ticket if they want to.
Everyone has to have a registered account. Only takes two minutes to set up then they can start earning loyalty points. Only one ticket per season ticket holder is allowed.