When you say on top of eachother I assume you mean that on the radar view it appears as if they are literally on top of eachother in the sky. They are military, they like to fly close, low, fast etc especially if they've been the OK to do so. I'm not saying thats the case here.

Though, seeing C130s fly close to eachother is normal, probably training. Refuelers can refuel other refuelers so seeing them really close is not abnormal either. I think C17/C5 flying really close to eachother would be an oddity though.

There is a layer you can enable on ADBSexchange that will overlay US fuel routes. It is labeled as US A2A refueling.