I believe you are right to worry about doing the job correctly. I think this kind of house (and anything else bigger, of course) is about the only one that will pay anything. Most RE photos are done by the agents and are fine for what they are but, in this case, you need to spend the time (if the owner doesn't have the time, than the agent should) and you should be charging enough so that you can do it right. HDR is the word here.
And NO, not the comic book type. The sort of HDR that allows you to have interiors that are not too dark (most of those are I think considering the amount of windows we are seeing) while keeping the windows from being totally blown. Also, I did not see a response from you on whether or not you have and used a tripod. You need one. A very good one for the HDRs and also for shots like the basement one.
A long exposure with the ceiling lights on is not the best answer for the basement shot but it can be done with just one flash. You just need to do multiple pops of the flash, turning slightly with each pop so as to light the whole room and have the ceiling lights on for just one (or maybe two) of the pops so that they show up up but are not the main source of light. I know it sounds hard but it's not that bad to learn. I've shot caves and underground quarries that way and it's not that complicated. Just practice in your basement. Mind you, it does help if you are comfortable calculating manually set flash exposure in the first place.
In addition to the other comments, the thing that strikes me most about these is the skewed perspective. If you don't have a wide enough lens to accomodate the space, consider making a panorama.
I'm not sure I quite get this comment. A wider angle will end up with even worse skewed perspective...
I like that the OP didn't use too wide a lens to do those. I recently put a house on the market and the agent did all shots with a super-wide that made the house look like something I had never seen. I had her re-do all the shots because I didn't recognize the place...
Back to the OP. You didn't do the best job but it is a pretty darn good one. TBH, the one that bothers me most is the first one. The outdoor shot. Who wants to live in the middle of a parking lot? There's got to be a better way to show the outside of the house.
Good luck.