Arrowverse Multiverse and Time Travel

Been thinking about this for awhile now, just seeing if anyone can shed some light on this or just add some ideas.
Ok, so we all know the basics of general time travel theres generally only 2 ways it can work.
A: Changing the past will effect the future in unforseen ways.
B: Changing the past creates an altenate branch of reality. (A new multiverse)
The Flash and Legends have already showed us that time travel in Arrowverse works as option A, so when The Flash or Legends time trival have they been going into the past/future of earth 1 or have they been going to different alternate earths? Considering how when Flash changed the past it also effected his future i dont see that as the case. However right before Sarah, Lois, and Brainy set off for earth 16 that is in the year 2046, Sarah says the legends had been there before just didnt know it was an alternate earth. Which kinda implys traveling to the future is traveling to an alternate earth. Kinda confuzing figuring out how it works, best thing i can come up with is the multiverse spans in the infinite with each universe having its own seperate timeline. But if that was the case how would there not be multiples of the Source and monitors instead of just 1 guarding them all