According to AW&ST 23rd June, the four B'ees will be accompanied by two KC-10s and are "expected to refuel around 10-12 times each during their crossing." I assume this (perhaps rather large) number of tankings reflects a prudent requirement to top-off regularly to ensure they will always be within some kind of diversion range.
The party "will be joined by a C-17 and at least one Marine Corps KC-130J in support." I assume the KC-130Js will inter alia provide tactical tanking and airborne security detail during the UK flying.
LFH