What will happen if you have your 15yr old girlfriend at your house and im 18 but her mom doesnt want her here and shes pregnant?

If the legal age of consent in your state/country is more than 15years of age, then it is unlawful sexual intercourse and this is a criminal offence. Your age can mitigate the response of the authorities and/or any sanctions...

It depends on where you are, it would be wise to seek a free consultation with a lawyer (where everything you say is protected) the lawyer will know the best course of action. She's a minor and you're not. So it's illegal. But I think it's very kind of you to stay with your girlfriend and help support her and her baby. Most men will probaly run away after they get their girlfriend pregnant. Get a lawyer incase anyone says anything to the police.