Red dead will sell the most followed by Cod then Battlefield and Assassin's Creed,in that order.

Lifetime it will probably be RDR2 > CoD > Ass Creed > BF. It wouldn't surprise me if CoD beat RDR though.

More to the OP though, which suffers the most because of the crowded month...... there will be no way for us to know. But, I think BF is probably at the highest risk of being lost in the hype around the others. Ass Creed probably has some risk as well. CoD doesn't have any risk, as it is always the biggest release of the year. Nobody is going to miss it. RDR is so highly anticipated that nobody is going to overlook it.

All of this assumes that RDR hits the stated release date. I think there's a 50% chance that it is pushed later into the fall. If that's the case, then there's probably enough hype to be had by every release in October.

There are three theaters to consider.

Europe, America, and Japan.

With a lot of these games Japan will not have much impact, but as a Ubisoft game A Creed could make up a lot of ground there. I suspect that how A Creed holds up will depend on Europe.