Welcome to planDisney, Kelly!
I have a 2-year-old as well as a very adventurous 5-year-old, so I am in almost the exact situation as you are. My oldest child is currently obsessed with
Space Mountain, and I know that my 2-year old has a few years before she can reach the height requirement.
Kelly, Rider Switch Service is completely separate from your Lightning Lane entitlement. So if you wanted to ride, say,
Slinky Dog Dash, you will only need to reserve one arrival time through
Genie+.
Once your Genie+ arrival time rolls around, visit the Cast Member at the entrance to the ride before you hop in line to get set up with the
Rider Switch Service. The Cast Member will scan your son's and husband's MagicBand or admission card to add an extra Lighting Lane entrance for that ride. You and your son can then proceed into the Lightning Lane. Once you exit, your son and husband may then head into the Lightning Lane by scanning their MagicBand or admission card. No additional purchase or reservation is needed on Genie+.
I hope that this put your mind at ease a bit, Kelly. I know that my son will be so disappointed when he can no longer ride everything twice, but I think he has a few more years before his baby sister is up for the thrill rides.
Have a wonderful holiday!
Sarah B.