You are deploying link aggregation groups.

When deploying Link Aggregation Groups (LAGs), it is necessary for all ports in the LAG to operate at the same speed to ensure consistent performance and avoid issues with load balancing. Multi-Chassis LAG (MC-LAG) allows for the use of member links that span multiple physical devices, offering redundancy and higher bandwidth by combining the links from two separate devices into a single logical LAG.

References

Juniper Networks Technical Documentation on Link Aggregation Groups

Juniper Networks Technical Documentation on MC-LAG