why if un (means masculine) and then doua and not dui?
Because this noun is neutral. If a noun is neutral, then in singular is with un, in plural with două.
Palton is a word that comes from Russian or from other language?
The Russian пальто also comes from the French paletot.
From French paletot, from Middle English paltock, of uncertain origin. https://en.m.wiktionary.org/wiki/palton