As already stated this is difficult to answer as it depends on a number of factors however, in general what would happen is that should a tenant pass away (regardless of whether they are a sole or joint tenant) a succession takes place and the tenancy will usually pass to their spouse or partner. So in your case, should you or your husband pass away it would transfer to the other. It is worth noting at this point that only one succession can take place per tenancy.
In the rare event that both you and your husband passed away at the same time, a succession would still take place and one of your children would be entitled to succeed. The act mentioned above does not state that the successor needs to be over 18 and so children can and do succeed to tenancies. It is at this point that the Council would look into the best way to facilitate this which could include your elected carers taking the tenancy in trust until your eldest child reaches 18.
Either way, as you mention the property is adapted for your sons needs, it is unlikely the council would elect to rehouse them as this would incur a further cost to adapt a new property (unless there was severe underoccupation). It would be worth speaking with a housing officer however it is unlikely they could give you a difinitive answer.