Answer to no.1; Obviously a pneumatic mortar, but I have no further info.
Answer to no.2; That is an Italian heavy gun - I'm not exactly sure of the calibre - in a so called De Stefano carriage. The De Stefano system was designed in order to make use of a large number of older large calibre guns, mainly taken from naval ships and lacking modern recoil systems. The De Stefano system was NOT designed for transportation per se, but as a substitute for a proper recoil system: the wheels rested on a short rail, and when the gun was fired, it rolled back on the rails. Quite ingenious, but with obvious drawnbacks, the main one being that whenever you needed to make a really serious traverese the rail system had to be rebuilt, of course taking a lot of time and effort.
Answer to no.3; That is a real gun indeed, it is a Austro-Hungarian 3.7cm Infanteriegeschütz M.15
Check it out at: http://www.landships.freeservers.com/37mm_infanteriegeschutz_m15.htm
Interesting, thanks for that Arie! If you look on NavWeaps, it lists only one model of Italian 10" naval gun, a 1908 model used in a class of armoured cruisers:
I doubt it was that gun as it would have had a modern type cradle and recoil mechanism.
However, there was an older model of 10" gun not mentioned on that site, that was fitted to some Italian central citadel battleships in the 1890s when they were refitted (replacing older 17" 100-ton guns with the more nimble 10-inchers). I have drawings at home of Armstrong naval gun mountings of the period, I'll have a look tonight. IIRC, those guns were fitted to old-fashioned slide mountings in hooded barbettes, so would have lacked integral recoil mechanisms.