Daleksfearme,
I can sympathize with you and what your brother in law is going through.
I, too was a victim of being struck by a motor vehicle several years ago and I still have not fully recovered.
I was in a coma for five 1/2 months, lost my left eye, ligament replacements in both of my knees, I have a mesh band in my abdomen, and too many more injuries to mention.
When I awoke from the coma and the physicians told me I probably wouldn't walk again for at least a couple of years; I told them, they have no idea with what kind of woman they are dealing with. I told them that when I leave this hospital I will be walking. Of course they laughed and looked at me like I was crazy.
I spent another four months and countless surgeries in the hospital.
But, you know what, the day I was discharged from the hospital, I walked out, be it with a cane; but I did it on my own two legs against all the negative odds my physicians were throwing at me daily.
The best advice I can give to you and your brother in law is stay strong and more importantly stay positive. Do not take no, can't, impossible, and improbable as an answer or excuse. Positivity is so very important. You won't believe how much the mind plays into the recovery of the body.
If a doctor or physician says something can't be done or that some treatment/surgery is impossible; don't just accept that. Find other doctors/physicians and get more opinions. Your brother in law has nothing to lose by getting different opinions.
Also, do your own research. Check around and see what other options are available.
It is a wonderful thing that you are doing by taking care of and supporting your brother in law. Support is vital when someone goes through a tragedy.
G@d bless you and your family
A speedy recovery for your brother in law
And if you need any advice or support don't hesitate to contact me.
Take care, be strong, and be well.