Three kids you mean?
Charles bought his open (Highgrove) via the Duchy of Cornwall in 1980, so it’s owned by the Duchy rather than Charles personally. He has rented it from the Duchy ever since.
Interesting, Parliament had assumed that that Charles would live in Chevening House in Kent, which had been left to the government in the 1950s on the basis that the PM would decide who got to use it. Charles preferred to arrange his own accommodation however, and so Chevening House is now assigned to the Foreign Minister for their use.
QEII bought a house for Andrew and Fergie (or rather she bought a plot of land and a house was built on it). Andrew sold it to a Kazahk businessman (in a not at all dodgy-looking deal 👀 ) in 2007.
And Edward and Sophie lease Bagshot Park, a mansion in Windsor that Queen Victoria had built for one of her sons to live in. It had previously been leased to the Army, but they relocated and the house became vacant and was leased by Edward the year before he and Sophie got married. He allegedly pays £90,000 a year to lease it and paid £5m to extend the lease for 150 years (where did he get that money? Most likely funded by QEII, I would imagine?).