My parents will be in Edinburgh staying on Leith St. Is there a nice not too expensive restaurant I could suggest to them? They love oysters and other seafood but it doesn't have to be limited to that. If it were a place that wasn't too noisy it would be beneficial for my father. Also a wine shop near there for my mother to pick up a few bottles for the cruise they are taking from there.
TIA.

The Cafe Royal in West Register Street is pretty good- It's an upmarket pub. Just quarter of a mile down Leith Walk, there is what is arguable Scotland's best deli- Valvona & Crolla.

It has a nice wee restaurant too, and a good wine section- albeit nearly all Italian.

Finally, whilst I see Cenntotre being recoomended, it's competitive cousin Vin Cafe is pretty good too.

ISO? does this mean something?

The Cafe Royal is good as has been suggested.
Just up the North Bridge from Leith Street is Hunters Square and there you will find Creelers Restaurant which is very good for seafood. www.creelers.co.uk/creelers-edinburgh.html

Fishers Bistro who are well known in the Shore have now a restaurant Fishers in the City. This is in Thistle Street and is relatively close to Leith Street. www.fishersbistros.co.uk/uni/main.html

Valvonn and Crolla in Elm Row (Just downhill from Leith Street) have a good selection of wines however if you would wish some cheaper varieties there is also a Threshers Wine shop in Elm Row.

The Thistle Hotel, right ?

Can't offhand think of anything to add to others' suggestions, but please note that V&C is not open in the evening (unless they'll be here during the festivals ?).

Thresher's on Elm Row is pretty rough so I'd advise them to stick to V&C for buying wine.