Hi, I am a non-JW married to a witness. We have no children together.
Since your children are teen/preteen, and you have had a sudden awakening/change of heart, I suggest you make NO ALARMING MOVES. This sets off both the cultist and the teenager radar.
I think it is too late to stop the baptism of your daughter. I do suggest you go along and allow it to be the enthusiastic event it is supposed to be. It will be like a "coming of age" for your daughter and will be significant in the context in which she was raised. I suggest you attend, take pictures, and take her out to dinner afterwards to celebrate.
Where you can step in is afterwards, when the baptism glow has faded and the reality of relentless proselyzing week after week, year after year hits home. That has GOT to be a grind for the modern teenager.
Besides the GREAT suggestion for "Teach your Child to Think", I strongly recommend Hassan's "Combatting Cult Mind Control." The ex-witness books are very good for ex-witnesses. For those of us on the outside, Hassan's materials can save us years of misunderstanding and missteps.