If Lind is your general, allow female soldiers in the law and policy screen to get a dialog that will make you encounter Mia.
When Mia is in your barracks, talk with her when you have 1 blue slimegirl and 1 green slimegirl in your monsterhall, and Jackies events advanced so that she and Lexi are at the monsterhall.
Leneth is recruited directly in the command center screen. It requires the events with Jackie and Lexi, and 1 small harpy and 1 big harpy released at the big farm.