You can take a couple of routes:
- Merge their skeletal meshes together and have them share the same root. Export one animation sharing the skeletal mesh
- If the bicycle doesn’t have animations (as in simply following the player as a static prop), you can create a leaf bone that stays with the root object of the character. That way you can simply attach the mesh to a socket/prop bone. You can animate the leaf bone off root based on how you need the prop to work with the character.
Based on what you need, it can be okay, but it’s generally not a good idea to combine skeletal meshes as it makes them a lot less flexible.
If the issue is to be able to select/move/manipulate the objects together, a blueprint will go a lot further!