Growing up in the US, children commonly say things like "Me and Johnny went to the store." Although it sounds perfectly normal to many people, it is considered terrible written style (and also bad style for public speaking), and grade-school teachers make a great effort to break kids of this habit. The only acceptable written form is "Johnny and I went to the store."¹ If we transform that word-for-word into Russian, we get the sentence «Иван и я ходили в магазин». Although every Russian will understand such a sentence, it is not the most typical way to say it. Instead the more common way is:

The phrase «мы с Иваном» is actually ambiguous. It can mean "John and I" or it can mean "We (a group of two or more people) and also John". The same holds true for the phrase «мы с ним», which can mean "he and I" or "we [two or more people] along with him." For instance, if my wife and I are having pity on our poor, miserable bachelor friend, John, I can say:

Although the second translation is the more natural way to put it in English (and thus the better translation on this occasion), the first translation captures the idea that John is included in the concept of мы in the sentence.

On the other hand, if I go to the movies with John but my wife does not come along, the same construction just means me and John:

The same ambiguity holds for the phrase «вы с Иваном», which can mean "you [one person] and John" or "you [more than one person] and John. For instance, let's say I'm talking to a female friend about her son Женя. If I want to ask whether she often argues with him, I might ask:

Or if I am taking to both her and her husband, I might say the same thing with a different meaning:

The same holds true for phrases with они, which can be interpreted a variety of ways. Let's say I'm talking about my female friend who is feeling sorry for another female friend. This sentence could result:

Of course, if my friend's husband also feels sorry for Vera, we could have a parallel sentence:

The same situation also of course applies if my friend is a man:

To review, the phrases «мы с ним», «вы с ним», «они с ним», «мы с ней», «вы с ней» and «они с ней» are ambiguous in that they can refer to groups of two or more people.

¹ Actually, the teachers do too good a job of breaking us of that habit without explaining the situation more thoroughly. In fact many teachers overgeneralize and just teach their students that any time they are tempted to say "me and you" (or any other combination of "me and..."), they must replace it with "you and I" (or "... and I"). Even very educated people — sad to say that among them are my own mother and sister — thus will say things like, "Just between you and I, I think that is a bad idea." The correct thing to say in that context is "Just between you and me..." But just try to convince them of that... it's a lost cause.

² In this context with the third-person plural pronoun, some native speakers prefer «Ей очень жалко Веру, поэтому она с ней часто ходит в кино», but in rapid speech the «они с ней часто ходят» form is entirely possible.

³ In this context with the third-person plural pronoun, some native speakers prefer «Ему очень жалко Веру, поэтому он с ней часто ходит в кино», but in rapid speech the «они с ней часто ходят» form is entirely possible.