It usually seems expedite is for the benefit of the US citizen/resident, not the beneficiary. I think it’s a long shot, anyway, as she probably had anxiety before she met you and has survived. Being with you isn’t a fix, but merely a temporary solution that could put her at ease for a little while.
You need to get your tax debt straightened out, as NVC will be looking at your taxes. You also will need to be able to support her, unless you can find a reliable sponsor. It sounds like you have an uphill battle. I would suggest doing your best to secure a job so at least you have some income come NVC time..and work on setting up a payment plan for your tax debt if you haven’t yet.
I think this would be pretty irrelevant. Your brother has always had Down syndrome and has been taken care of this whole life. They likely won’t care much about a knee surgery for your dad. Especially with you being unemployed, which means you have sufficient time to handle these things on your own in the interim.
Honestly, it seems like you’re reaching for anything here to get an expedite and none of it seems like things USCIS will see as valid reasons..just my guess. I mean it’s totally worth a shot and free to try, so you may as well! But if you do actually get the expedite, you won’t have as much time to get your finances in order. So it may be in your best interest to just take this wait time to handle all that. Wishing you the best of luck with that.