Yes I have just come back a couple of weeks ago from lindia thalassa which is part of the chain. You can use any of the 3 sister hotel facilites during your holiday. They are all really good hotels I would say go for it!
Pefki Islands is a fantastic place,and you won't be dissapointed.
As stated,you can use all the facilities of it's sister hotels-Lindia Thallassa one side,and Island Blue the other.
Whilst there,make sure you attend the fantastic greek night at the hotels Elias restaurant,YAMMAS