I'm sure this has been asked before but I can't find it in the search, so I apologise in advance.
We are booked on BA293 LHR to IAD (and the return 1 month later) in First, this is a redemption flight with an AMEX 2 for 1.
This is normally served by an A380 with a 14 seat first but recently (3 times over the last week as I can't see further back in Flight Radar 24) has been swapped out for a 777-ER (Reg G-VIIC, G-VIIV, and G-YMMK) which looking on planespotters.net could be mean a 14 seat, 8 seat or in the worst case no first at all. Looking on the seat booking page for our flight it looks like first is full. One thing to note is we need to fly on the day we have booked or the next day really so would more than likely accept a downgrade over a rebook.

So finally after the long preamble here are our questions,

#1 How do BA decide who to downgrade (we assume we as silvers on redemption will be quite near the top of the list to be shunted)
#2 Do they shunt down the cabin? i.e. would we go to club, someone in club to prem and some one in prem to eco? or would it only be the first passengers that would move to whatever seats are available?

As for refund/compensation were not really that bothered at the moment as this flight is the start of a 30 day trip and getting to America is more important than fighting with BA but we assume we would only get the difference in Avios back.