Put house in parents name to protect when first married, now want to change it to mine and wifes.

To protect the house when I first bought it and for the much better mortgage rate, we put the house in my parents name and they took out a refinance on their house to buy my house outright. I pay all taxes and refinance payment since day 1. This was done in May of 2004. Now that my marriage is great and I have kids, I want to put house in me and wifes name and take a mortgage out for what is owed on it still. My question is do I have to "buy" house from them? Can I somehow do it so the payments I have made to them for the refinance look as a downpayment? I would like to avoid the 15-20+ thousand downpayment and closing costs. Plus if I buy the house from them for what they still owe on refinance, this will look like they are giving me house for below marke (about $100,000 below). I know I need a lawyer to do this, but have no idea how much this is gonna cost me and how to start. Thanks.