"Who do they have this from?"
Translation:ממי יש להם את זה?
That's not correct. In modern Hebrew את has to be used in יש/אין sentences.
There's some debate about its grammatical correctness in academic circles (see also the Wikipedia article), but the bottom line is that it would be almost incomprehensible to say "ממי יש להם זה" without את.
Both are inflections of ...ל. https://en.wiktionary.org/wiki/%D7%9C%D6%BE#Inflection_2
In short, לכם is for second person (you) plural masculine, להן is for third person plural (they) feminine.