Don't have sex with Antonina throughout all of this.
1. Get to threesome with Marina & Dasha.
2. Repeat 6 times.
3. Talk to Dasha, then Marina about their mother.
4. Marina says she needs time (70+ hours) to learn massage.
5. Go to gym (their house, 2nd floor) at 19:00, watch.
6. Once the scene start repeating - talk to Marina in the main hall.
7. Repeat 5 & 6 until Marina has sex with her mom. (Antonina will have to be without sex for 200+ hours).
8. Talk to Marina, meet her in Antonina's room.
A few notes:
* This is based on the original, Russian QSP. Your results may vary.
* If you use a cheat mod, pressing '++' to advance the time will
NOT advance Marina's massage training, nor Antonina's celibacy. Either use QGen or QSPSaveEditor to play with the variables;
Antonina without sex
Code:
data['события_начальница_часы_б_траха']
Marina learning massage
Code:
data['события_марина_учит_массаж_часы']