"Those singers, which are beautiful, are famous."
Translation:Azok az énekesnők híresek, amelyek szépek.
amelyikek = amelyek, the former might be considered incorrect.
In general, whenever you can use amely, you could also use ami, but not the other way around. It's a but complicated when to use amely, so here's a Nyest article on it:
It's in Hungarian, but gives many examples (with the numbers in parathesis.) These examples should help you with your question. The starred words (*amely) denote that that construction is incorrect.