Not completely.
You can use import project to bring skeletons into the same project. You can drag some things across skeletons, like bones, slots, and attachments, but not everything. Moving something across skeletons is actually very complex under the covers, as there are many dependencies and corner cases to handle.
You can also use import project to bring an animation from a project to an existing skeleton, but many requirements must be met: the skeletons must have the same bones, slots, etc as described in the docs. This is ideal when you have a master project with the skeleton set up and you want to have multiple people create animations (but not bones, slots, etc).
One solution could be to export to JSON, then merge the JSON as you need. You'd probably want to write a tool to do the merging. FWIW, the JsonRollback tool shows one way to manipulate JSON data using libgdx (or JsonBeans). There are also many other JSON libraries. The important part is that the end result makes sense to Spine and the Spine Runtimes. Eg, if you have an animation that shows/hides attachments for a slot, you have to make sure that the skeleton has the slot and attachments. It's not a simple problem, but if you focus on just what you need, it may be worth the effort for you to build such a tool.
Otherwise you might consider a simpler approach, eg split your 2 skeleton project into separate projects with 1 skeleton each.