Not sure if this will help anyone at this point, but you can get the A ending for one character and the B ending for the other character in one playthrough.
Ending A is unlocked for the first character you doki doki per playthrough. Ending B is unlocked by doki dokiing a character after doki dokiing Riisu.
For example:
Doki doki Nanako
Continue with Nanako's events and final mission
Skip to the ending once the prompt appears at your house to see Nanako Ending A
Continue the game and doki doki Riisu
Doki doki Chiru
Continue with Chiru's events and the third Kurona fight
Skip to the ending once the prompt appears at your house to see Chiru Ending B
