Hello veganyum,
so you have 3 skeletons in 3 separate files, and you want to add a 4th skeleton of a house? Why do you want to combine it with the others? To place them standing on the house patio?
You then mention that you want to combine skeletons, which skeletons need to become one? Do you simply want to have one giant messy skeleton with the house and the 3 human skeletons as a bunch of additional bones?
Or do you want to be more sophisticated and combine the guy fishing with the walk and with the wife?
The first case is possible, but honestly I'd probably just import them in the same Spine project so that the skeletons are still separate but it's easier to animate them interacting with each other.
The second case is a bit more complicated. I think it would be better to keep them separate, especially if the number of bones, their placement, the structure or their names don't match.
In case you still want to go down the merging route, you will need to import the Spine skeletons all inside the same Spine project, then you can drag the bones and release them all under just one of the skeletons.
Import - Spine User Guide
As I mentioned, this will remove the constraints that you will need to recreate. After this you can import the animations from each skeleton into the designated skeleton.
In any case, wheter they are combined or separate, sure! you can animate just one part at a time and have its own special animation that your programmer friend can trigger!
