The third one has these legends:
Obv.: CONSTANTIN─VS P F AVG = Constantine II (son of Constantine I) as Augustus = emperor (with his two brothers), so 337─340.
Rev.: VICTORIAE DD AVGG NN + mintmark in the exergue (bottom part) that could be read by comparing with other coins.
I would suggest that the second one is an ancient imitation of a Roman coin (from northern Europe? North Africa?). The legends are kind of wrong on both sides, and the portrait, too, seems unusual. Any expert out here on Numista who would confirm or disagree with this ID?
And the first one (working backwards) has the legend:
Obv.: ?? IVL CONST --- (is this Constans or, again, Constantine II?)
Rev.: GLORIA EXERCITVS + mintmark •TRP•
Much of the reverse legend is gone, but I don't see what else it could be.
As for the first one, IVL CONST would identify Constans ─whose full name is Flavius Iulius Constans─ rather than Constantine II ─Flavius Claudius Constantinus.
Constantine I "the Great" is Flavius Valerius Constantinus. Note, however, that there have been mistakes with those names (Valerius / Iulius / Claudius) even in official documents. I'm not sure about coins, but in all probality, your coin was issued by Valens.
It could actually be Constantius II or Constans. Both appear on similar coins, with that bust, that reverse, that mintmark (.TRP.), that legend beginning (FL IVL C..). The details of the reverse (standards and soldiers) can even be the same on similar coins of both rulers, of what I saw doing a quick search on nummus bible. I'm not able to find an element that could attribute yours to one or another...
So, it's probably CONSTANTIVS because his name has three more letters than CONSTANS and fits better in the space above and to the right, followed by NOB C. The full legend is probably this:
FL IVL CONSTANTIVS NOB C
with bold for letters that we can see at least partially. We can almost guess NOB C but it was very lightly struck. No doubt it can be read with a magnifier and playing with light at different angles.
