I'm unable to find a description in the rules of what happens to the target of a combat maneuver if that target has the grappled condition.
Example 1:
(A) has successfully grappled (B). (C) charges and bull rushes (A), beating the CMD by 10. (A) should, in theory, be pushed back 15 feet. Since (A) is grappled with (B), does (B) also move 15 feet? Does (C) have to make a bull rush CMB check against (B), just as if (A) & (B) were not grappled, but (B) was standing behind (A) in the line of the charge? Or does (B) stay in place and the grapple is broken by (A) being moved 15 feet?
Example 2:
(A) has successfully grappled (B). (C) knocks (A) prone by means of a successful Overrun or Trip maneuver. Is (A) still grappling (B)? Or has the grapple been broken now that (A) is prone?
I'm unable to find a description in the rules of what happens to the target of a combat maneuver if that target has the grappled condition.
You're not gonna find them. That is what we have human GMs for.
Example 1:
(A) has successfully grappled (B). (C) charges and bull rushes (A), beating the CMD by 10. (A) should, in theory, be pushed back 15 feet. Since (A) is grappled with (B), does (B) also move 15 feet? Does (C) have to make a bull rush CMB check against (B), just as if (A) & (B) were not grappled, but (B) was standing behind (A) in the line of the charge? Or does (B) stay in place and the grapple is broken by (A) being moved 15 feet?
Shooting from the hip, I would give A the choice of letting go of the grapple or not. If he does not then I would make C attempt to maintain the grapple. If he fails the bullrush is just against him. If he succeeds the bullrush is against both A and B.
Example 2:
(A) has successfully grappled (B). (C) knocks (A) prone by means of a successful Overrun or Trip maneuver. Is (A) still grappling (B)? Or has the grapple been broken now that (A) is prone?
I would say they are still grappled. You can grapple while prone just fine.