Combining Rider Switch and Fastpass?

Haven’t been to DL in 3 years since we nixed our APs, and I feel soooo rusty trying to plan for just one day! So, refresh my memory:

DH and I want to ride Space Mt, but our 2 girls (ages 6 and 1) won’t/can’t. Can we obtain just a single fastpass for my DH and have me use the rider switch pass? Or do we both need fastpasses?

I’m not sure if this helps but we have a 2 year old who couldn’t ride seven dwarfs mine train when we went. We had to all have fast passes to do rider switch together in the fast pass line. I think you have to all have fast passes to go in the lone together.

Assuming it works the same as at WDW, then you would just need one single fastpass and then you could use the rider switch pass. So you could get single fastpasses for multiple things at the same time that way. and figure out something else to do with the kids nearby.