Yes, you can.
You can create groups with the Milos you have now, any ones you might purchase in the future, or even ones that your friends and family have.
Milo packs are not pre-grouped when you purchase them so you can configure the group that works best for each Milo adventure.
You only need to make sure all Milos are running the same most recent software version.
With the current software (v.11, Summer 2024), Milo supports up to 8 in a group.