I doubt very much that any of the RF would go, as they would not want to cause distraction, or provoke accusations of muscling in. This is a pretty normal way for the RF to go about things (not invariable, but exceptions are few)
The German Chancellor did attend the IG in Dusseldorf, not sure about other heads of state in earlier Games. So I think it would be quite reasonable to expect the Sec of State for Defence (plus other defence ministers, plus others with relevant sports and disability portfolios) to attend, and probably the PM too.