Which 2 islands, Naxos, Paros, Sifnos, or Milos?

We prefer to stay away from huge tourist areas

Just to warn you that Naxos, Paros and Milos are in the top 5 of the most touristy and crowded islands in the Cyclades (after Santorini and Mykonos)

Also note that Naxos and Paros are in the Central Cyclades and Sifnos in the Western Cyclades.
These are not the same ferry routes, in summer there are some ferries which operate between these two parts of the Cyclades islands but the journey may be expensive and long.

You could also combine two islands that are part of the Western Cyclades.
These are:
Kythnos - Serifos - Kimolos - Sifnos - Milos - Folegandros - Sikinos

Apart from Milos, none of these islands has an airport.

Andros and Tinos are also two neighboring islands that could suit you.

And don't forget that apart from the Cyclades Islands there are almost 200 other islands that can be visited.

https://www.visitgreece.gr/

Yes there are so many. It is truly hard to decide. I chose those 3 because those were the only ones I really saw information about. I did see that I should try to stick with one chain of islands due to travel time. I'm open to everything. Basically, I know I want to go Greece to experience their culture, visit historical sites, see beautiful scenery, and eat delicious food.
I'm open to suggestions. I really don't want touristy places and based on the information that was just supplied, it seems my choices weren't the best.

Since Naxos, Paros and Milos have an airport this makes them more easily accessible but they have nothing more than the other islands apart from a more developed tourist infrastructure.

Even on these well-known islands, in September it is not difficult to find places away from the crowds, especially if you rent a car.
Naxos is not necessarily an island to avoid, it is the largest island in the Cyclades where many tourists stay in a small area at Naxos town, the port and capital, and go to the organized beaches between Agios Prokopios and Plaka (maybe the herd instinct?) but there are dozens of other places to stay if you have a car and don't feel the need to be close to restaurants and shops.

See here:

https://www.google.com/maps/d/edit?mid=1d7GZMjFODUlB8lf7EPSXQRwu-YXaKxw&usp=sharing

Same in Paros if you stay in Parikia or Naoussa.

Milos is specific given that there are few villages and the southern half of the island is almost uninhabited, it is a Natura 2000 zone.
As it is a volcanic island, many of the beaches are rocky. (with an often Instagrammed lunar landscape).

Anyway, by 2026 you have plenty of time to do your own research among the 22 Cyclades islands that can be visited by looking for real information, not that of social networks and paid influencers.

https://www.visitgreece.gr/islands/cyclades/

We are regular visitors to Naxos. We always visit in May to Mid June or September early October. These shoulder season times are not as crowded as the high summer period.
This June we were in Naxos until June 15. The town beach (St George beach) was not crowded. The rental beds and Umbrellas were 50% occupied and there are several areas for sun bathing on the sand. There was lots lots of area for additional visitors.

September will likely be a similar experience.
We also stayed at Plaka beach on the west coast. That beach is a couple of kilometres long where you can find lots of sand or chairs and umbrellas and was not at all crowded.

Naxos is a great destination with its old town, mountain terrain and villages and beaches.

You are going to be there after the high season is over.
The one thing that has changed over the years is it is necessary to make a reservation to ensure your table at the taverna you want to visit in the evening.

Here is what Naxos was like .
Naxos town https://www.flickr.com/photos/stanbr54/albums/72177720318203165/
Naxos Beaches https://www.flickr.com/photos/stanbr54/albums/72177720318216108/
Naxos at night https://www.flickr.com/photos/stanbr54/albums/72177720318406428/

Thank you everyone for the information! It is very appreciated.