Milton Keynes Dons boss Paul Ince followed up the signing of goalkeeper Willy Gueret with three more players before Saturday's 2-1 defeat by Bury.
Abbey, Howell and Navarro have all joined Milton Keynes
Another goalkeeper, Nathan Abbey, 29, joined on a one-year contract after a successful trial spell - having ended last season with Brentford.
Midfielder Alan Navarro, 26, joins on a one-year deal following his summer release by Macclesfield.
Also on a one-year deal is former Gillingham midfielder Luke Howell, 20.
Howell and Abbey were unused substitutes against the Shakers, while Gueret was in goal, although Navarro was not in the matchday squad.