I think Brian WILL be the only guitarist, as Jamie Moses has already said that he won't be in the band as they are having a "smaller band this time around".
It's only going to be one fewer, so to me seems a bit odd to drop the second guitar when they have had it for 20 years, Brian is usually a lot less flustered coming out of his solos with a second guitarist behind him, and these days it's pretty much accepted to have a 'hired hand' (even Bon Jovi have had a second guitarist behind Sambora for the past few years and JBJ often plays too making a third, and they have a lot washed in keyboards too).
Not complaining mind if Brian pulls it off
Interesting that Jamie isn't going to be with them, and he has said that it will be a smaller band.
It is quite possible that Spike may well play guitar on some songs and keys on others.