Hi Adam, I know far more about real ships than models, but my guess is that they are most probably scratch built. However, all the kit manufacturers have made kits of tugs, so these may well be from kits. Somebody else on here may well recognise them. 'Cervia' was the last tug built for Ship Towage in 1946 and I think there is a kit still being made.
On a personal note. with a degree of name dropping, the MD of Ship Towage, was the commodore of our local yacht club and I sometimes sailed with him, racing his Dragon class yacht, 'Hai Lung', that would have been in the 1950's. About twenty years later, I found 'Hai Lung' abandoned in a boatyard in Faversham. I bought her and gave her a complete restoration.