Ivan,
For that usage you could use any of the following:
"Welcome"
"Welcome to our community."
"Welcome to [name of your community]."
Actually, I used it as an admin of Telegram chat meaning welcome to our community. Anyway, thanks for your comment, Bruce!
Hello.
"Welcome to us" would not be used by a native speaker of American English. You could just say "Welcome." If you are speaking to more than one person you could say, "Welcome, everyone."