Does flanking grant combat advantage to all allies?

Question

Does a properly flanked enemy only grant combat advantage to the allies doing the flanking, or to all allies?

Answer 1

No

Only the allies in flanking positions get combat advantage.

However, there is a feat that allows a ranged attack to benefit from flanking allies. It's called Distant Advantage

There is also a feat for half-elf rogues that does exactly this called Group Flanking

Finally, there is Vexing Flanker, which does exactly what you are talking about without the class/race specificity.