No. Orders from different stores cannot be combined.
If you try to combine orders from different stores, you will see the following message:
Unable to combine the selected orders:
- The selected orders cannot originate from different stores.
Can I combine multiple orders going to the same address?
How to: Find multiple orders to the same recipient
How to: Combine orders
Can I combine orders after I’ve “Split” them in ShippingEasy?
What happens to a category tag when an order is split or combined?