I don’t believe there are any Sentinel guilds still left on the server. I haven’t seen any in the last year or so.
There are a few Night Elf guilds around! Moonlit Enclave is often in Stormwind.
My guild, Conclave of the Moon, can be found in Ashenvale primarily. You can read more about us here: [A-RP] Conclave of the Moon - Night Elf RP