It has to be a piece of clothing or armor that exposes you, not one of the underwear slots. For example the Rouges Rags you can buy from Shekka, the Slave Uniform from Zeng Shi, and others. Also make sure she has the heating upgrade if you don't have that one.
Scout Stations are the places with the checkerboard race line. With Sera you need to pick an option that you finish in the right hole, and then just wait and talk.
For normal Autofellatio, you need your dick to be at least 1/3rd your height. For continuation with Paige you just have to do more Yoga sessions to unlock visiting her apartment (which is next door to the right), then after a few visits there you unlock sexing her.
I don't know what to do with Sera? (it's still just "make love" option) what do you mean hole?
Also it turns out I can't have along big dick since it seems Sera taps at about 20inches. And I need at least 40 inches to get the 1/3 of my size (I guess it's Yoga for me then)