Ephesus is near Kusadassi, it's one of the more northern resorts (not norther Turkey, but northern with regards to the holiday coastline).

I went to Ephesus nearly two weeks ago, it's a long drive from anywhere but Kusadassi, Didem & perhaps Altinkium. I thought (my personal opinion only) that Kusadassi was a horrible place. A large concrete jungle, think Magaluf, perhaps larger, even had tower block hotels & apartments.
BUT, you can do Ephesus as a one day (Ephesus only) or two day (with Pamukalle as well) coach trip. It's cheap & let the coach take them there.

I stayed at the Aegean Dream Resort Hotel in Turgutreis. Great hotel, beach front location. I don't know if your parents have any mobility problems, but this place had fantastic disabled facilities (best I've ever seen in Turkey), everywhere in the hotel & grounds was easy to get around & lots of lifts & well marked steps ect. They had lots of ground floor rooms as well. We met 2 retired couple while there, they were on their second trip & had requested ground floor rooms, they also have walk in "wet room" type showers. It's all inclusive & has great reviews, there are loads on here. The hotel seems to attract less familes with children than most AI hotels (could just have been the season), there was a good mix of all guests, retired, middle-aged, young couples, familes with kids, disabled people, couples, large family groups, all sorts.
There is a huge market in Turgutreis every Saturday (biggest in the area).
There is a fishing village a few miles away called Gumusluk that has fantastic waterside restaurants, the one I went to even do a free door to door service from & to your hotel, the Aquarium, oh & great food.

Bodrum is well worth a day trip. Gumbet is better than Kussadasi (in looks) but best left to the teenagers.

Olu Deniz is great, but just a little hilly in the resort, but if they are fit it's great.

I love Olu, but the Aegean Dream Resort Hotel is better than any hotel in Olu. Never stayed in Lycia world so I can't speak for that place, but I think that's more aimed at young familes anyway.

The weather will be fab in September where ever you decide, probably THE BEST time to go. Intense heat has faded, sea is still warm & the kids are going back to school.

I'm sure others will be along with other favs.
What size resort do they like? Small, med or large. An example of places they really like would be good.

Take a look at Bitez - we will be there in September ('Sir' is 60+++ and I am getting there!) There is a lovely beach (man- made but pleasant), lots of restaurants, no rowdy bars or nightclubs (but you can find them in Gumbet and Bodrum if you want a change of pace), lots of local excursions to Turgutreis for the market, Bodrum for history, Epheseus and Pamukkalae, plus lots of local trips via the dolmus to Gumusluk, the Aqua park, Yalikavak etc....etc.....etc...

kimevans - I like the sound of the hotel you mention, they don't have any mobility problems (Though after a bottle of wine between them you could be forgiven for thinking they have!). I don't think a large place is really them, probably midsize, they like to socialize a bit so need a few people for that.

Prawn - Was there a particular place in Bitez you have/are going to? Sounds like it is close to a lot of the places kimevans mentioned, they like a bit of a day trip to see all those kinds of places.

Depends what they are looking for in a hotel. Check out the Bitez forum for more advice. We tend to stay in small hotels, bed & breakfast, and eat in the local restaurants but each to his/her own. Last year we stayed at the Small World...it is small, quiet, clean, welcoming. The only reason we are not staying there this year is because we got a good H/B deal for the whole month at the Kassandra - never been there but willing to give it a try. There are hotels to suit all tastes in Bitez, from 2 star to 5 star. Take a look.

Prawn - We would want something good for them, a 4 or 5 star place would fit the bill, half board being ideal. Thinking about what has been said, it really is important that they are not miles away from all the day trips you mentioned, they love that sort of thing.

The Aegean Dream resort Hotel is a (Turkish, lol) 5 star & very resaonably priced.

cafc83 - check out the hotel reviews and resort reports on here. They will give you a good idea of where may suit them. Everyone has there own favourites but they will give you a good overview.

Good luck with your search.

I would recommend the hotel Hemera in Side.It has great reviews and is only 5minutes dolmus ride from the old town which has roman ruins including an ampitheatre.They could also take a 3day trip to Cappadocia,an amazing place.I would read all the hotel reviews rated 4 or 5 stars then see what they prefer.

belek has some super 4 and 5 star hotels..it has a nice beach..a small local town....and well placed for excursions both east and west of Antalya.
also its not far from antalya airport...and a trip into the old part of Antalya is wonderful..the ancient harbour is a romantic spot and full of great restaurants.

Can only second what Shirley has said , belek is great ,smashing beach,great hotels ,and handy for any day trips to places of historical interest. Me and the wife are away there on sunday for the fifth time in two years .

Bluepeterno1