Need help setting up ER8411 in a specific way

This is for a home network, and I'm just using the stand alone interface.

The "owner" is insisting on forcing a dual internet setup with load balancing(one line in is fiber, the other is a really terrible cable connection). This is, unfortunately, complete crap for my use and is causing me constant disconnection and ping and other connection issues, but I'm stuck with this because the "owner" is stubborn and refuses to listen to any sort of reason, so am trying to configure the router to allow my two PCs two things:

a) bypass the load balancing all-together and have all traffic routed through the fiber

b) have priority over all traffic so there's no risk of bufferbloat and reducing latency as much as possible and getting as stable of a connection as is possible

I tried to do the following: assign my two PCs static IPs, then put them into an IP group with rule that forces it's traffic to priority, and to use only one connection. But it's not working, and I don't know why, the router just behaves like its using default settings and the two PCs are still getting their traffic split between two internet connections.

I'm not an expert in this at all, at the moment I'm just trying to get workable internet.

Is my understanding of how to bypass the load balancing correct?(assign static IPs, assign those IP/mac addresses to a IP Group, then use routing/policy routing to say all traffic from IP GROUP to specific WAN?

How about my understanding of QoS? I have it setup like this, where One is the IP Group I attempted to make. I'm not 100% sure if DSCP is correct, I read online that CS7 is the highest priority.

Please help me get this working, I am pulling my hair out over how I have fiber internet RIGHT THERE but I can't get a stable connection because the "owner" insists on a ridiculously pointless and pain in the ass load balancing setup.