the Home Licence will (with reservations) - as it is planned at the moment - include 50 Endpoints. This quantity should be more than enough for non-commercial use.
Nonetheless an additional purchase may be possible, but only if you have a good explanation at hand. Otherwise you need to upgrade your licence.
Agreed with Ian. Since the kids no longer inhabit our home, we'd only ned 4-5. A houseful of kids might neeed as many as 20, so I'd think you could do 20 or 25 without cramping anyone's style.
Yeah, 50 is probably too much for free... not talking about anyone on here, but it could encourage some to "cheat" the system. 10 should be more than enough for a home user.