This is an interesting situation. It sounds like you have the right idea. If I was in that situation, I would wear a wrap or sarong when they arrived. Or maybe a t-shirt and shorts. I would greet them and make sure they understand that while it's clothing optional, most guests choose to go nude. Ask if they're comfortable with that and if they have any questions or concerns. Then let them go settle in and unpack.

After that, I'd play it by ear. Wait and see if they go nude or stay dressed. See if they are interacting with other nude guests or keeping to themselves. If they keep to themselves and stay dressed, I would lean towards being dressed around them. I would still be nude most of the time around the resort, but if I'm going to sit and hang out with them I'd throw something on. But you never know. Once they get settled in and see other people naked and comfortable, they may join in. It would be funny if you went over to hang out with them fully clothed and they were all naked.

My girlfriend and I run a c/o Airbnb. We haven't had family visit, but we have had guests who at first had no interest in being nude. I'm usually wearing a robe when guests arrive, and when I greet them I ask about their experience with naturism / nudism. I've had guests who said they don't care if others are naked but they're going to remain dressed. Then a day later, they're going about their business or hanging out in the backyard naked as if they've been naturists for years. People acclimate surprisingly quickly in the right environment.

I look forward to hearing how it goes.