Jehovah's Witnesses, could someone become a member if they refused to use Jehovah and instead used Yahweh?

You are right in saying that we are not sure how Yahweh (Jehovah) pronounces his name. But the name Jehovah is known worldwide as the Almighty God. There are many gods people worship, (even Satan is called a god in the bible, the god of this world) but they should only be worshiping the true God Jehovah. His name separates him from false worship. We are his witnesses and known as Jehovah's Witnesses not Yahweh's Witnesses even tho they are the same one. Once someone learns about our wonderful God they will want to use his name every chance they get.