Unfortunately, no, there are no split gates. You can name them 19L, 19 and 19R, and set the radius accordingly. However, they are treated as separate gates. I don’t think ATC will be able to detect the overlap; so you may end up with a B747 in 19 and an A320 in 19R. However, I have not seen MSFS airports congested enough to validate that theory lol. You may still want to mark them like that for realism purposes (let’s say for people flying on VATSIM).
Jetways are 1:1 with gates. A jetway node has a single gate attribute, hence you can only assign it to one gate. Also, if you mark a parking type as GATE_, you must assign a jetway to it. This means that you either create 3 jetways for 19/L/R, or make one of them a GATE_ with a jetway and others as RAMP_GA_ with airstairs. For example, you can make 19 as GATE_HEAVY and 19L/R as RAMP_GA_LARGE.
For taxiway links, I’m not quite able to visualize the layout, but typically for the intersecting links, it really does not matter which taxiway name you choose, as long as there is a named link between the two. So, let’s say you have a long taxiway A, and there is taxiway B merging in the middle of A, creating a T intersection. You’ll have two links from B going left and right onto A. In such cases you can name both the links B.