While acknowledging that i do not know anything about programming and some suggestions might me too much of a trouble or even impossible to implement, I give you my list:
1. New buttons for the dungeon "Brand All" and "Sell All" girls.
2. Accommodation option could use some improvement. I am not very certain what it does to be honest. But I was thinking of something like the higher the level the greater the upkeep for it and the bonus (happiness for the girl, a small boost in client income etc).
3. Could something be done to clients that are taken in the dungeon? I am not suggesting anything like expanding the way girls are, just that you can:
a. have a small chance that the family will ransom him
b. can brand him as a slave and put him to work in the brothel/whatever as a cleaner/guard whatever. I could bring you an extra symbolic bonus (2 gold or reducing filth) or on the contrary he could just cost you 10 per week because you have to feed him and it doesn't produce anything.
c. in case you can brand them as a slave then be allowed to sell him (for random sum like sons are).
4. maybe something similar to 3b could be done to the sons. And thus instead of being sold right away they are placed in the dungeon. It's not much of a change but gives you the sensation you are more in control.
5.a Expanded history for the girls. As in:
number of:
-clients served
- Monsters defeated
-times raped/defeated by monsters
-number of daughters/sons she's given birth to
-number of weeks she's been working for you
-times she’s given birth
- as far as i understood form previous posts it's impossible to show the total income the girl has brought you

6. From my experience money is made too easy in general so any money sinks would be great. I have no idea if that you agree with this point of view or if you willing to address it, in case you do here are more suggestions:
-Ad more sliders (similar to advertising) in the brothels section like
Upkeep per week , it shouldn't give a great bonus maybe a small boost to girls happiness or client income or reduced rate of filth etc
-upgrade brothel which should cost something like 50 000 per level. Again it doesn't have to give you any significant bonus (maybe change the background picture), a couple of free extra rooms etc
- more weapons upgrades/levels for gangs
Long shot here, but maybe more options for girls in general:
-plastic surgery
-send on vacation