So would you tell R that if you want the 2 points, decline the illegal batting?
FB already gave the correct ruling, but just to spell it out for a novice and fellow Ohioan: A caused the ball to go into the end zone, where it subsequently became dead: independent of A's foul, the result of the play is a safety.
The penalty for a foul committed in the end zone is a safety. So if B accepts the penalty it's a safety; if they decline the penalty, the result of the play is a safety. Were I white hat, I wouldn't even ask, as the explanation of why they don't have any options would take too long.
The dead-ball foul by B is a separate issue. Since A will kick off after the safety, B's penalty will be enforced 15 yards from the 20, and the free kick should be from the A35 yard line, as Tom said.
A final teeny technicality: since the down that resulted in the safety did not have a legal kick, we don't refer to the teams as K/R, but as A/B (2-43-3). Keep up the good work!