Splitting Bandwidth

Dear Friends

I have 20 customers each 10 are grouped on separate router (group A), and (Group B). i have one ISP and i like to split the bandwidth of 3 Mb total. 1 MB for (Group A) and 2 MB for (group B). i brought a third router that works as a splitter then i connected both groups to it, (Group A) on ether2 and (group B) on ether3 and my ISP to ether1. i tried connected all ports with bridge adn putted queues on ether2 and ether3 but the problem is that my bridge doesnt allow the queues on ether ports to work.

Is there any way to accomplish my goal without using any addditional hardware, also NAT options are not allowed on the splitting router.

i appreciate your valuabe help…