1. Make sure you have sleeping pills and women's viagra.
2. See if the command to spy on Tamara's dad shows up at 23:00 on Saturday/Sunday.
3. If not, check the Kitchen at 18:00 on Saturday/Sunday to see if the option to spike Tamara with viagra is there.
4. If neither of those two options are there, try checking Tamara's room at 19:00 during the weekday. That's Monday - Friday.
5. If there is no option to spy on her phone/text her dad with her phone, then you need to try talking to Tamara AT WORK during the weekday. See if there is an extra option to "Discuss the incident" at all.
To expand on this, I did a speedrun through Tamara's chain just now. In addition to the 5 steps above, in case you haven't actually gotten to the point where Tamara tells you about her dad sending her dick picks, you'll need to speak to her dad in his room during the weekend, at night. There is one dialogue where you ask him what's wrong. Apart from that, following the above 5 steps ensured I got through the spying chain.
The cheat item menu does not put sleeping pills in your inventory, so you DO actually need to swing by the pharmacy in the mall to buy some ambien. Also grab the women's viagra from the sex shop while you're in the city.
1.After Tamara discusses her dad's dick pics, you will need to buy the ambien AND GIVE THEM TO TAMARA. Now you will be able to do the first peek event during the weekend.
2. After the first peek event, you will need to spy on her phone at 19:00 during the weekday to see one more text message.
3. Do the 2nd peek event.
4. Talk to Tamara at work during the weekday, "Discuss the incident"
5. Spike her with women's viagra at 18:00 in the Kitchen.
6. Now you can repeat the peeking events until Tamara sits on his dick.
From there you can try to trigger the threesome events. The trips for that one are fairly simple, I just repeated the following during the weekend;
1. Have sex with Tamara at 18:00 in the hall.
2. Have sex with Tamara at 22:00 in her room.
3. Do a peek event where Tamara sits on his dick.
That's it, repeating those 3 over and over eventually triggered the threesome scene in Tamara's room during the sex scene.