First of all PRAY. Ask that the Holy Spirit open their hearts to the Truth.
How well are you versed in Apologetics? I was able to use my knowledge to gently answer all the questions my, formerly anti-Catholic, boss asked me. Over time he came to realise that be had been misled about what Catholics actually believe.
Learn to ask them questions about why they believe certain things that are different to Catholic teaching. I suggest you study up on the Catholic position, but by turning the whole thing around and being the one to ask the questions, you are putting them into the position of having to think about what they believe.
Lastly, when you have any specific objections or questions you need answered, start a thread here.
God Bless