"The rules I've mentioned only apply to opening up an independent restaurant in the middle of court building grounds.
There are a few other options you can take in case the review doesn't go your way; one is to work in an already established restaurant within the Order. With your skills, it wouldn't be too hard for you to get in. I can make a few suggestions if you want.
The other is to be the siblings' legal guardians. When they pass their entrance test they will be resettled inside the Order and they will also have the option of bringing family members with them if they have any. It isn't restricted to blood relatives.
Based on your interaction I can see that the sentiments you share for each other are genuine and I'm willing to vouch for you which would be enough to get you resettled with them.