Does legislation have to be proposed by the WH? Or can members of Congress propose bills?
No. Bills are only introduced by members of Congress. The president can propose a legislative agenda, but Congress can act without the president and then hope that he signs the bill. Congress voted several times to repeal Obamacare while Obama was in office, obviously without any action from him. He vetoed each of the bills, of course.
Congress can even enact laws without the consent of the president; with a super majority, they can override a presidential veto. It happened once during the Obama administration on the 9/11 victims bill (allowing victims to sue foreign governments).