custody of my kids

Me and my wife were living alone (separate from my parents) with our two kids first one is almost four and other is 2 and a half years of age.
My wife and i got separated (not divorce) after my brother in law and I had a fight. we were living in a house near in-laws and she refused to come with me and stayed at her parents. Now she is demanding a house in her name to come back and have custody of children. Her father sent a demand list saying until you build a house in my daughters name you will not be allowed to talk to them. I want the custody of my kids until she agrees to come back or decided to go to court. can I have the custody of my kids by any law while there is no divorce between us?
please help.
Sincerely
WK