The way I remember it, was that MySQL was sold, then some time after, MariaDB was created as a fork, and you could switch between them. Then at one point MariaDB diverged sufficiently that you could no longer "effortlessly" (kinda) switch between them, by now they're separate but MariaDB's origin is still MySQL obviously.
Yes Monty started MySQL then forked when either Sun or Oracle acquired it.
My, Maria, and Max are his kids. There is MaxScale which is a L7 SQL proxy/loadbalancer