you can use sqm with cake and per-host isolation option and it will automagically distribute the available bandwidth fairly between all devices/connections.
I did a test in a virtual environment with VirtualBOX (5Mb link and 3 VM Ubuntu).
At first it does get the balance. Of course, the division is not the same, but it is very similar.
just to be sure.. i don't see this in your screens..
To enable Per-Host Isolation Add the following to the “Advanced option strings” (in the Interfaces → SQM-QoS page; Queue Discipline tab, look for the Dangerous Configuration options):
For queueing disciplines handling incoming packets from the internet (internet-ingress): nat dual-dsthost ingress
For queueing disciplines handling outgoing packets to the internet (internet-egress): nat dual-srchost
please mark as solved if you are satisfied with the results
Him, the test_WAN_* variants of the scripts are really not maintained, do I would recommend switching back to either piece_of_cake.qos or layer_cake.qos (if you want to use DSCPs to prioritise some traffic), and I would try the manual configuration of per-internal-IP fairness, as recommended by @jesanor
Why these are not in the default scripts, you might ask? Well, to configure this one needs to know in which direction of the SQM'd interface the internal network is located, otherwise one risks to configure per-external-IP fairness, and I am not sure anybody ever wanted that