To obtain futa pills I believe the intended workflow is:
In the Haunted House, you are supposed to hide (click text or hit spacebar) when she gets close. Though when she catches you get a couple of bonus CGs so worth getting caught at least once. Keep the light on Astrid until the bar fills up. You need to do this 3 times and after this the Vampire will show up when you return to your room. NOTE - You do not actually get Vampire Spit here I think it is a visual bug, you get it on the 4th time of completing the Haunted House after doing anal with Astrid. Also if Dr. Frost has her child before handing in the Vampire Spit will be locked out in the after birth loop so this cannot happen)
You then use them in the Studio > Porn
So put simply complete the Haunted House 4 times with doing Anal with Astrid, hand in the Vampire Spit to Dr. Frost and visit Anna for Porn in the Studio
NOTE 2 - If Dr. Frost has her child before handing in the Vampire Spit will be locked out in the after birth loop so this cannot happen)
NOTE 3 - Anna will call you Nathan in the Futa CG not your player given name
All NOTEs are bugs which will be fixed in 1.8B in the next days or week.