I'll cite an actual Classical example:
itaque quoniam aliter dis immortalibus est visum, cum mortem ne recusare quidem debeam, cruciatus contumeliasque, quas parat hostis, dum liber, dum mei potens sum, effugere morte, praeterquam honesta, etiam leni possum.
And so, since the gods have decided otherwise, and as I must not even shrink back from the prospect of death, I can, while still free and while I am my own master, escape the tortures and indignities that the enemy is preparing, with a death honorable and even merciful.
(Trans. Yardley with minor corrections by me.)
Using this example yields:
Tui potens es.
You are your own master.
It's more succinct than the above example, lacks the slave-master connotations, and is completely gender neutral. The plural is easy, too:
Vestri potentes estis.
This usage of potens is outlined in Lewis and Short, with this example and similar ones cited:
Having power over, ruling over, master of a thing; with gen.: “dum liber, dum mei potens sum,” as long as I am my own master, Liv. 26, 13, 14: “sanus mentisque potens,” in his right mind, Ov. Tr. 2, 139: “potens mei non eram,” Curt. 4, 13, 23: “potentes rerum suarum atque urbis,” having made themselves masters of, Liv. 23, 16, 6; so, facere aliquem potentem alicujus rei, to make one master of any thing, to give one the power over a thing: “consilii,” id. 8, 13, 14: “imperii,” id. 22, 42, 12: diva potens Cypri, that reigns over Cyprus, i.e. Venus, Hor. C. 1, 3, 1