Hub and spoke SDWAN and QoS

Hi to all,

can somebody explain how to handle QoS and traffic shaping in hub and spoke sdwan where spokes are connected via two tunnels (mpls and Internet). The part that is confusing me is that branches have different Internet download speed and we have one Internet link in HQ. Sum of all branch download is higher than HQ upload. 

How to guarantee bandwidth for different classes? how to use max bandwidth if other branches are not using it? How does HQ handles these different speeds in SDWAN? 

Where do Traffic shaping policies and profiles fit in here?

regards