Blimey, could you build them a separate house to live in?
Space for them to get away from each other/you. So either bedrooms rooms big enough for them to chill out in with friends, or a separate den or two. Plus as many bathrooms as you can manage. Cheap carpets in these if not laminate floors.
A room off the hallway for all their Stuff - coats shoes football stuff etc etc so it is out of sight. I know someone who built a mini utility room by their back door with a shower so anyone really filthy from rugby, biking etc could leave the mud there. Was great for muddy dogs too.
Hardwire internet access into every room they will ever enter, plus more power points than you could possibly think necessary. It was made clear to me that Wifi was NOT good enough for serious gaming and you need hardwired ethernet cables in the wall if you are to avoid cables snaking across your Dream Newbuild Home.
Underfloor heating EVERYWHERE, ideally wet-system, then when they throw their wet towels on the floor they still dry beautifully.
If humanely possible, a laundry chute...my dream, never fulfilled...