The second set of photographs are very good, and it's interesting to see shots of the mess deck of a Motor Launch, which is something seldom captured.
The photo featuring the railway viaduct ought to be traceable — I don't have a lead on it as yet. The one entitled Unknown location maybe Malta , Naples or Maddalena? could well be Marseilles in fact, which 575 was known to have visited. It was at Corsica and all over the Western Med as well as the Adriatic. There is also something of a mystery in this photo as it clearly shows MGB 91 going by. This boat was an American built Elco and part of the 7th MGB Flotilla which served in Home Waters (Portland, Dover, Lowestoft) and is shown in the December 1944 Navy List as a Target Towing vessel at Lowestoft. So this photo must be later than that obviously when it may have been tasked to Southern France at some point ahead of being returned to the USN in July 45, and being laid up at Gillingham until 1947 (at least according to the records).***
The C.O. of ML 575 from October 1944 onwards was John Barfield, with Lt R. A. Wright and Sub-Lt D. W.Trevan shown as the officers from July 1945 onwards. None of the crew shots feature Lt Barfield, but owing to the timeframe involved, they could have been taken under the later tenure of Lt Wright, or failing that they may then be ML 170. ML 170 was part of the 9th ML Flotilla along with MLs 172, 173, 174, 175 and 176.
In the photo of MLs ML575 and 554 alongside one another in harbour the crew are in non-whites, with wet weather gear, so this doesn't look like Malta.
*** On reflection this can’t be MGB 91 so another possibility is that it may be an Italian MAS Boat. There were MAS boats of the Italian Navy recorded as attached to the Royal Navy by late 1944, but I have yet to find evidence of one numbered 91. There were some USN PT boats in the Mediterranean theatre as well, but again none with this number. Also the boat in the photo doesn't appear to have radar or weaponry.