Sample:
Dave, will you take James and Bill to be your step-sons? Will you provide for them and care for them with love and affection, offering them encouragement and guidance, and will you live with them and their mother, as love and respect would lead you, in the role of stepfather and husband? Dave says, "I will."
James and Bill, will you take Dave as your step-dad? Will you give him love and caring, accept his encouragement and guidance, and will you live with him and respect him as your step-father? James and Bill say, "I will."
If you don't care to use "step" you may substitute "parent" or "child." The format is the same for mothers and daughters.
Popular Readings (available by searching the Internet)
I Corinthians 13 (Love is patient, love is kind)
Ecclesiastes (To every season)
Apache Wedding Blessing (Now you will feel no rain)
Kahlil Gibran (Stand not too close to one another)
The Lord's Prayer (Catholic and Protestant versions)