Isn't more correctly "I am a Muslim and he is a Jew"? I just ask, I'm not a native English speaker.
I believe you are correct, yes. "Evreu" is a noun, and the adjectival form of "evreu" is "evreiesc". Likewise, "Jew" is a noun, and the adjectival form of "Jew" is "Jewish".
From "Romanian Grammar" by Dana Cojocaru:
The simple conjunctions şi and iar can be difficult for an English speaker, since they both can be translated into English as 'and'.
Şi equates and integrates two elements: Dan şi Maria petrec Crăciunul cu familia anul acesta. Dan and Maria are spending Christmas with their family this year.
Iar integrates and contrasts two elements simultaneously: Dan şi Maria petrec Crăciunul în România, iar eu stau în Franţa. Dan and Maria will spend Christmas in Romania, and I will stay in France. Dan îmbodobeşte pomul, iar Maria găteşte. Dan is decorating the tree, and Maria is cooking.
In normal usage, there is a tendency to use iar instead of şi when adding two actions (sentences), even if the contrast is not very strong - in other words, there is a tendency for iar to accept copulative meaning: Dan împodobeşte bradul şi Maria îl ajută. = Dan împodobeşte bradul, iar Maria îl ajută. Dan is decorating the tree, and Maria is helping him.
A useful rule of thumb is that "iar" can be translated as "while", whereas "și" cannot.
Yup! Same works for Serbian. "si" would be "i"; "iar" would be "a". Also if somebody was trying to find the difference for "insa" and "ci": insa=ali, ci=nego (it's Serbian/Croatian/Bosnian), might work in other Slavic languages, but I speak no other Slavic language but my mother tongue :D