The high level overview, assuming you're doing a single stream with all this, and the 2 gaming pcs are going at once, will be both capture cards go into the streaming PC, each gaming PC goes to one. In OBS you'll add both as sources and setup a scene where you can see both.
The mic setup will depend on the layout and if you're planning to drive the Rodecaster from the streaming PC or one of the gaming PCs (I recommended the streaming PC).
This is a lot of data bandwidth used between 2 capture cards, and 2 HD webcams. Assuming this is all USB you're going to want to make sure the streaming PC has more than one USB Root Hub on the motherboard, and try to split the USB devices between mutiple root hubs to make sure nothing gets overloaded (see https://help.elgato.com/hc/en-us/articles/360042824631-Two-Elgato-USB-3-0-Devices-on-one-Computer-Two-USB-3-0-Root-Hubs-Needed for a little more detail on that - there's a link in there to a tool called USB Tree viewer that'll let you see what gets connected to each internal hub on your motherboard).
I think you meant to tag @drifting ocean, @past basin





