How to set up Zyxel Keenetic Giga II for two active pppoe?

Question

ZyXEL

There is a Zyxel Keenetic Giga II router. Three providers are connected: 2 wired (pppoe) and one 3g modem. all three providers with static ip. On my own, I managed to set up that all three seem to work at the same time only in the given order. Ie, for example, I can connect through any of the three ip via rdp from outside. But one has only to change the priority of one wired provider in order to set another as the main default. immediately everything collapses and only one new main provider works, including for some reason it is impossible to connect through the previously available 3g modem. How to set up two active pppoe so that you can connect from outside using any of them?