Hello Milly and welcome to the site.
I'm sorry for the circumstances which brought you here,but you can be certain of plenty of support and advice for both of your cavaliers.
There are members here who have experience with both epilepsy and SM.
11 months is very young to have to cope with SM.
I presume you have had him Mri scanned and have good veterinary care and insurance?
the best advice I can give,based on my own experience with SM,is to make sure you do a blood test for liver function before putting him on medication and monitor every few months as some meds can be tough on the liver.
There are others here who can give better information of their experiences of medicating and managing younger dogs with the condition.
As for surgical intervention,I chose not to go down that route myself,I didn't feel that there was a hospital with the expertise and experience to carry out the surgery in Ireland and it is a very big undertaking.
It's understandable that your head is in a spin and you need to allow time to absorb the news and research the condition.
Anything we can do to help...just ask!
Sharing my sofa with Holly, Ivy,Lilly and Hazy.. and never forgetting our beautiful Daisy who reached the bridge too soon.