Hi Steve,
I don't know the particular hotel you are staying in, and I have only been to Marmaris a couple of occasions - but I do know Turkey very well and have stayed in most of the major resorts.
The one thing I can tell you is Turkey's pavements can be very difficult to negotiate - even for a sighted person. They often have very steep kerb-drops, and there are sometimes very large potholes, loose slabs etc.
Turkish drivers often drive very erratically (both cars and motorbikes) and will often expect pedestrians to jump out of THEIR way - so always cross the road where it is absolutely safe to do so.
Another thing to watch out for is that many hotels use cheap tiles around their swimming pools making the surrounding area VERY slippery - they will occasionally put up notices warning people of the problem, but that is no good for you of course. Watch out too for the odd broken tile around a pool. It may be wise to buy some non-slip sandals with grips that they could wear around the pool.
Obviously, good sunglasses which cut out the damaging rays will be an essential, but other than that I can't think of much else in the way of tips.
If you go to Turkey again, it may be an idea to take them to Olu Deniz as they have a lovely lagoon for swimming which is very safe (and they can't swim too far out); they have a water park nearby with big slides; a flying boat and parascending; horseriding and even paragliding which I think a blind person would get a lot of pleasure from.
I hope you all have a lovely holiday.
Strawberry