Now without further information from yourself about the test results from the lumbar puncture, this limits my ability to assess what type of meningitis we have. This is quite important as we can see bacterial, viral, protozoa (Toxoplasma, Neospora), and steroid responsive forms of this condition. Furthermore, if the treatments that have been used have failed, knowing which is present +/- culturing that spinal fluid to ID any bacteria present is even more important for treating him.
That aside, I have to say that if he has lost motor and sensory function to his back legs, then time is ticking here. And if you have not already updated his vet on this (your history is not clear on this), then they need to know ASAP. This is because the longer he has no use, the less likely he will be to regain it. Usually in these cases, it is related to the condition directly, related to spinal issues (hopefully those have been ruled out already), or is due to the condition causing inflammation or swelling of the brain. In regards ***** ***** the ones you have noted are appropriate but if he has swelling of the brain then he may need to be treated for that as well. And to do so, we tend to need them hospitalized. So, he needs to be admitted if he has not been already.
Overall, based on what limited information you were able to provide, we are in an urgent situation for your lad. If he has lost use of his hind legs, he needs more aggressive treatment to reduce brain inflammation, swelling, as well as treatment for the primary cause. The sooner this is done, the better chance we have of regaining function. Though at the moment, we do have to be wary that his prognosis is quite guarded.