All very nice looking N frame guns. In many cases, the dash-2 engineering series is the largest, so many, if not most, guns of a particular model will be dash-2's. The M27 and M28 are cases in point. The M27-2 and M28-2 were made for 20 years (1961-1981), your M25-2 for 16 years (1961-1977), and your M29-2 for 18 years (1962-1981). They're not rare, but it doesn't mean they aren't worth anything special. Since it is an earlier version of the model, obviously it's older, and generally puts them into the P&R era for magnum calibers and the pinned era for others (Pinned barrels and recessed cylinders ended with dash three guns in 1982 for these models), and your M25's pinned barrel with the dash 5. Three of my guns are dash-2 (M27-2, M28-2, M29-2), and I have two no-dash models, but they are of a later release date than the above models (M57 and M58 didn't enter the market until 1964, and had engineering changes already made to earlier production models). I also have a dash-1 and a dash 3 gun, but they are K frames. Your "S" prefix gun is getting to be more special, indicates manufacture prior to 1968, when the SN prefix changed to "N". My M57 and M58 are "S" guns.
It's no matter, I like these older guns myself and seek them when looking for a particular model. Yours are exactly what I'd want to collect, and you've got a great start with four of the best.