No, you cannot group several boxes into a single package, as you would run the risk of partial loss.
No transport company allows the shipment of several packages strapped or sealed between each other because they cannot guarantee the safety of the contents.
The only option would be for you to put the small boxes in a larger box, so that only one package travels with a single label.
Keep in mind that shipments must be labelled in order to be transported. If you contract the shipment of one package, there will be only one label and the collection note will only mention a single package, meaning that there is no way of proving that several packages were collected. If any parts are lost, no claim will be accepted.
If you are going to send several boxes, it is best to contract the shipment for several packages.