He snorted when Regulus spoke about Harry, he was so far beyond caring about his brother's opinion of the Potters - that was just one area where they would always disagree, and it wasn't worth it to get upset over his brother's opinion - that he'd accepted James was enough.
Sirius pressed a light hand against James' back when he sat down with him again, he could tell that despite the way Remus and Regulus were both giving James suggestions for what he ought to do at this upcoming meeting, they both had more questions about this plan of Dumbledore's - not that he blamed them, of course. It just didn't bode especially well for the future.
"Remus is right, Snape and Moody are part of this for a reason you should use them as much as you can if you need to - they can help get others to accept these changes." And true they might have only brought James into the fold to manipulate him and his family, but they needed him whether they would admit it or not - if they weren't going to work with Harry, then James was their best option and they needed people to accept James as much as James needed them to accept him.