GG The answers to all your medical questions would be, the data is not yet complete but that there are suggestive and often too anecdotal reports of benefits. It surely helps some specific rare pediatric seizure types. There is good evidence for CNS alterations from pot, that is why people use it. For any specific patient whether those alterations would be beneficial would be best settled by trying it. But it is illegal. I cannot usefully speculate if it would have helped his brother but from what I understand the standard available medications did not.
As to whether it can be legally prescribed for the conditions supported by Mayo's website.. NO and that is what this was all about.
105 Peer-Reviewed Studies on Marijuana - Medical Marijuana - ProCon.org
Here is a list of 105 studies of marijuana in various forms with some data.
As of now 1/2 the states allow medical marijuana and a few allow recreational marijuana.
Here is the list (prior to this year's votes) on the states and the specific details of their laws as to what conditions and requirements must be met for medical marijuana.
23 Legal Medical Marijuana States and DC - Medical Marijuana - ProCon.org