I received UI for migraines and PTSD in 2017. Personally in my belief, your initial appeal was denied and that probably has caused some of your issues, RO's do not like admitting mistakes.
There is a wrinkle on remands. The RO is not required to increase your husband's rating or pay back pay until the remand is completed by the RO. A remanded case is supposed to receive top priority but that is not always the case. You could look into filing a writ of mandamus in your case. This informs the VA that the board has required them to expedite your case. I am not sure exactly how this as done as a lawyer filed mine. Maybe there is someone here who has filed one and can chime in. Bertha maybe.
Is your neurologist willing to file a letter that your husband is now too disabled to work due to his migraines and PTSD? This would also help in getting SS disability.
I am sorta concerned about you getting a lawyer, you have done a lot of work yourselves and a lawyer would take 20% of the benefit he helps win.
I believe your chances are good, especially since the board seems sympathetic to your case.