I use the serums all direct, if that's what you mean? Which oils do you mean?
I've gotten into essential oils lately and think I'm going to incorporate them into my do it yourself products. Lavender is a natural preservative, so I'm thinking of adding that.
I like my orange cream the best (the face cream). But my bio with gaba is really feeding my skin. I use both.
You can mix almost any actives together, but you are supposed to keep the acids away from the non-acids. So I would make a serum using nothing but acids, and then a cream with nothing but skin food and hydration.