Hello ejo84;6403045. So sorry you are going through something stressful. Can you fill in some blanks? How do you know that your husband is a "sex addict?" Is that a conclusion you came to on your own based on observations or has he told you he was diagnosed by a psych professional? If so, is he participating in some sort of addiction therapy?
You question "underage" issues. I have zero education in sexual addiction but adult sexual addiction and pedophilia seem to be two distinct problems. Are folks living with sexual addiction at higher risk for engaging in predatory behaviors? I have no idea...I think you'd need to ask a licensed sex therapist. For example, I've read that there's a growing trend of young men being addicted to pornography...unhealthy yes...but doesn't necessarily have anything to do with minors or predatory behaviors.
How long have you been married? Were you unaware of these sexual "addictions" before he moved in with you and your daughter? Has he said or done something to indicate to you that he would threaten your daughter's welfare?
With regard to your daughter, I recommend educating her on bodily autonomy and boundaries etc. That will serve her well everywhere in life.
With regard to your questions, I recommend consultation with a marriage therapist who has experience with sex addiction. You can go individually or with your husband. That is to say, if this is a diagnosed disorder.
I hope you will find the info and support you need. Take care