Hey Howdy Hey Sally and welcome to planDisney!
Sounds like you are going to have a really great time on your next trip coming up in May! With the switcharoo, with your sister and your husband, this can make things a little confusing but overall to your question it depends.
As far as your reservation goes, most rooms can sleep up to four adults, so as long as your only have that number or less you do not necessarily have to change their names out on the reservation. The issue comes up when your husband gets there, if he wants to have access to getting in and out of the room himself, then he would need to be added to the reservation. This would come into play so he could either use a MagicBand or have
MagicMobile set up on his My Disney Experience account to get in and out of the room. Since it is only one night I would leave it up to you.
A few tips going forward for your trip. If it is just you and your sister for the first leg of the trip, I would recommend checking out
The Grand Floridian Spa. Treat yourself to any of the special treatments and massages for an upscale and rejuvenating experience during your stay for an extra special treat. Of course, in the parks, I would highly advise a trip over to EPCOT to check out
EPCOT International Flower and Garden Festival. This festival has so many great flower and garden displays, gardening tutorials, live entertainment and some
great seasonal food and drink offerings throughout the park. This festival is growing to be one of the more popular springtime celebrations you don't want to miss!
I hope you continue to have fun with the final weeks of preparation for your upcoming trip and don't hesitate to reach out if you have any other questions!
Have a Magical Day,
Nick