Hello Everyone,
I have two connections from different ISPs that are using PPOE Servers for authentication. I have PPOE 2 users on each ISP line. I want to merge these two ISP Links into a single Links so that I can dial all four Users from a single line. I have RB Gr3. Please see the image for clarification:

Looks like you should setup 2 separate nets. One for each pppoe. Easiest way is to just use 2 routers, but its possible with some rules to have 2 going.

You can use vlan if you just have one link down to switch.

If it's really just 4 users in total and not just a simplified example, you can use bridge filter rules or even switch chip rules to forward traffic from each user to the corresponding ISP-facing port and to prevent traffic from leaking between the two ISP-facing ports. The latter is critical, otherwise the ISPs might get really upset.