I certainly don't see anything legally questionable about their above quoted T&Cs. It's clear and it's fair. Furthermore, as already stated, for only €2 a seat (standard seats) That's an additional €16 round trip for a family of four (less if the kids are under age 12). I really cannot grasp what the problem is here.
AerRyan reckons he/she paid €6 per seat. The nearest I can see to that figure is the Priority seating although it is quoted in their T&Cs as €7 per seat. That is an extra service. Again, I don't find that particularly expensive. Finally, at €11 per seat for Priority and extra legroom I consider that a very fair price. My airline of choice charges €20 per seat for that (not that I use that option mind).