So an overlord or union could carry refugees? Or a warship? As in BoI?
Yes but I did the maths for the Mule and the most efficient solution if you have to go through long distances is to use the cargo bays but to put some equipment in it (steerage and stuff like that), otherwise, you won't go far (from an interstellar point of view).
So the Mule has 3 Cargo Bays of 2,715; 2,715 and 2,714 tons.
Let's go for full Cargo Bays (easier to do).
One will be converted to transport passengers and the others 2 be kept for supplies (trust me on this one).
With 28 infantry men needing 5 tons, you can put in 2,715 tons, 15,204 people.
With the steerage, 1 ton of supplies allows 200 man/days; with 5,429 tons, you can get 1,085,800 man/days or enough supplies for a travel of 71 days.