A king is like two twin beds together, but without the crack in the middle. When my mom moved her third girl out of her room, we pushed two twin beds together and let the youngest sleep in the middle. She didn't seem to mind, but I sure wouldn't expect someone older then two to appreciate being in the middle that way.
Their "family size" wouldn't handle our family, and I wouldn't want to afford it either. Might be handy with a little one in your room, but washing that double king sized bedding.....every time the baby spit up or overloaded a diaper????.... would be a pain!
I really like the adjustable baby bed right next to mine. Baby sheets are so easy to change n wash, and she can roll over to me, and I can roll her back....or snuggle. Best of both worlds.
I like co-sleeping until they are weaned and sleeping through the night. I like letting them sleep with a sibling at some point after that.....and before there is another baby.
I'm not opposed to sharing under other circumstances, but that is not my reality, and I live in the real world.
Edited to add I cannot imaging spending 200 bucks for a single fitted sheet either!