maybe this is what acinq is doing or bluewallet with their lndhub?
LNDHub would allow your family members to use your node's channels for all of their transactions. They wouldn't need to open any channels. Instead, they would need to deposit coins to an address generated by your node. Then, they would be able to spend exactly the amount they deposited. They could also receive coins without depositing anything.
today i had this idea how i could give access to friends and family to my node. what if they install the latest new shiny lightning app on their smartphones (with the ability to open channels - not acinq/bluewallet and the others) and then open private channels to my node. that would mean they can profit from my "position" in the network, but don't need to be online. then setting the fees for the private channels to zero (or one could charge for the service, by setting fees on these private channels).
I don't think that there is a better solution for c-lightning. The biggest disadvantage is that they would be limited by the liquidity in the channel between you and them. Setting the fee to zero for private channels won't affect outgoing transactions.
That's impossible, channels inevitably get closed when the other party becomes unreachable, like in the case of the client crashing or the system rebooting. Why do you need non-closable channels anyway?
In such cases, channel becomes inactive. Closing means settling the balance on-chain. It wouldn't make much sense to close the channel only because the other party went offline for a short period of time. Still, it is not possible to create a channel that cannot be closed.