In Inkscape a path can consist of multiple (potentially open) subpaths that all share the same fill and stroke settings. Is it possible to do this in Sketch? I tried to make a union of three open paths but it fails.
In Illustrator this is called Combination Path. If I create one and save it as SVG, I can open it in Sketch, and it works as you want it to - similar to a group, but with shared style settings.
The problem is how to create this in Sketch directly. I'm not sure if there's an easy UI/shortcut way to do this. Using Layer>Combine>Union works to a certain degree, but it would outline open paths and perform boolean operations with all of them. One workaround is to create a union of two objects and drag your other paths inside this thing in the list view. You can then delete the two initial objects.
Or just use Inkscape, Illustrator or else to prepare your shapes there, then import them as SVG.
As earlier comment mention, the equivalent to Inkscape Path > Combine in Sketch is Arrange > Group Layers.
Both are a type of grouping where all information is maintained about the paths you group. In Inkscape you can still edit the different paths individually after you apply Path > Combine, the same is true in Sketch for Arrange > Group Layers.
You can try joining the paths by selecting both paths and the going to Layer->Path->Join. This might not work as you want since when you join the paths, it will unify them. This might cause another vector to be created. It depends solely on the vectors.