Just saying that FS1 is a bit shaky when it comes to theory proofs.
That goes both ways. It's shaky at proving that there are,
and at proving that there are not.
The thing is, lack of canon evidence here is likely proving the point, as if there
were multiple jump points, the GTVA's plan to seal off Capella wouldn't necessarily work so well. After the events of FS1, if it were the case that the Lucifer was using a doubled-up jump node (since they tell you about it, they must then therefore know of it), they'd probably have to deal with that possibility when sealing Capella.
On second thought, the GTVA doesn't take into the account the possibility of the Shivans using unstable nodes either, so...
My gut says that "no, it's not possible to have doubled-up jump nodes" though, at the very least between GTVA systems.If you're introducing some new systems with weird node topography, then by all means case go ahead and do whatever works for your stroy.