Hi,
I am a single Dad and getting remarried soon. I have two sons (14 and 11 years old). I love them very much...

How do I start the conversation with my sons about me getting married soon?

Do they know the woman?

I think more background info would be helpful.

I had stepdaughters with my late husband and I have stepchildren with my current husband. In both cases the children were not surprised when WE told them we were planning to be married because they spent time with me and their father(s), knew me, didn't have any problems with our relationship. Of course, there were questions about where "we" would live but I didn't threaten their relationship(s) with their father(s) in any way.

In both cases I didn't live with their fathers prior to the marriage. I don't know what your situation is.

My late husband was single for 12 years, my current husband for 6. In both cases the children were concerned about their father's happiness and the fact that they didn't want their father(s) to be alone.

Do they know the woman?

I think more background info would be helpful.

No, they don't.

I'd give them a chance to get to know her a bit before you announce that you're planning to marry her. Announcing you're marrying someone they don't know might not go so smoothly.