You can use the plugin that is called “Moon Animator” to animate it in roblox. I prefer animating in blender so you need to import one roblox model (Here you can find how to do it with this plugin: Blender rig exporter/animation importer ) and just duplicate it with SHIFT+D and just work on them with not changing their origins.
Here is a tutorial you need to follow if you want to animate in blender: [Blender/Roblox] Adding multiple rigs in blender(and exporting animation to roblox) - YouTube