This one from White pages for D Provan from a search on White Pages Capetown.Automatically extended to search South Africa ..............if the search doesn't show anyone in the place you have used in the search criteria it automatically extends the search to the whole of South Africa.
D Provan 50 Algoastr Strand , Boland & West Coast , Western Cape 021-853-1459 (International dialing code is 27-21-853-1459)
021 is the Capetown dialing Code so this could be one of yours.
The only G Provan I could find was from Boksburg, Gauteng.This is one the towns a few miles outside the Johannesburg boundaries, but, of course, it could also be one of yours.
If you Google for White Pages South Africa you may be able to find others. Try using the full first name as well for the search - I only used the initials in the searches I did.
Hope this is some help. Haven't made much progress re my Provans so far unfortunately and wasn't aware of any of my family connections that were in South Africa so would be interested to know a few more details re your connections and if they were from Kilsyth originally.