Being married to a woman and her niece at the same time

Q: I want to marry my wife's niece who is 25 years old. I am 35 years old. I know that I cannot have both at the same time, but I have heard that one can marry another woman without giving divorce if he and his current wife have mutual consent not to have any physical relations. Please tell me if I can marry my wife's niece as I stopped all physical relationship with my current wife.

Writing and saying talaaq three times

Q: I wrote three times I give divorce my wife in front of my mother but my wife don't know about that but we again together. Then my wife asked divorce I say 3 time divorce and same time wrote 3 times I gave divorce and 2nd or 3rd day in front of lawyer I sign on divorce paper again but within 15 days we again together. After that we sit together and say each other we are doing nikah again. So kindly let me know are we still husband and wife and now we have a son also. Please guide me thanks.