In a dust chocked world where the rich live in air ships and the poor in muck a dethroned princess and desperate criminal must join forces to stop a megalomaniac from seizing absolute control.

Hate to choke on a detail but doesn't muck connotes mud, slime -- subtances that are wet? ?So how is all this muck possible in ?a dust-choked (ergo dry, arid) world?

Hate to choke on a detail but doesn't muck connotes mud, slime -- subtances that are wet? ?So how is all this muck possible in ?a dust-choked (ergo dry, arid) world?

The last draft of the logline lacks an inciting incident and a detailed description of the goal.

Why must the princes and criminal take action now? What event sets them on their path?

Secondly the wording indicates a dual protagonist plot. If so, is there a specific reason for that?
It's strongly recommended to stay away from multi protagonist plots, so?unless it's a necessity for the story it may be better to make it about the princes or criminal instead of both.

If only one of them is the main character then best to change the wording, for example:
...a dethroned princes with the help of a criminal must? or ...a criminal with the help of a dethroned princes must...
This makes one character seem more like an ally than protagonist.

Last thing,?how will they avenge their families and know that the tyranny is over? Kill the overlords, banish the overlords into the muck? What is the end game?