It's entirely possible to stream 4 different stadia accounts on a 1gig connection with no latency issues :).
1 Gig spectrum. Netgear nighthawk AX11000 Router.
Right now my set-up is two TV's mounted with Chromcast ultra side by side. Specific devices linked to each. I have a PC that's also linked by HDMI and various tablets and my google pixel.
I was able to get two instances of chrome running on two accounts by setting one to priority and standard priority the next. Dragging one window to the second screen. The only downfall to this? The controls. The sync of controllers only recognizes one set.