It really should be, but note that it is pronounced "ha-la-vam" (not to be confused with "hel-bam", which is spelled the same), which sounds strange. I wouldn't go as far as Sharon to say that we never say this, but it's rare.
well, "חלבם" is not really a word we use in Hebrew. Better keep it two different words: "החלב שלהם" or "החלב שלהן".
you put them together correctly, we just don't say it that way..