The Duchess of York and Her Majesty got on okay and spent a fair bit of time together at the residence she shares with The Duke of York. I would think she will be in attendance.
As for Earl Spencer I would not be surprised if he attended, but I also wouldn't be surprised if he didn't.
I would be quite surprised if Michael and Carol Middleton weren't there.
^
Of course, that isn't the definitive list. Personally i wouldn't be all that surprised were the Middleton's not invited, nor the Spencers. The line has to be drawn somewhere.