Help please! Family problems!

I'm 9 weeks and 5 days pregnant. It wasn't planned but me and my boyfriend love each other so much and are very excited about it. When i was 7 weeks we decided we should tell our families but decided everyone and anyone else can wait till after our 12 week scan and made this clear to our families as we live in a small town. His sister how ever decided to tell quiet a few people so word got out. I was quiet upset as i felt like telling people had been taken out of our hands and we had to hurry and tell all our close important friends then as we wanted them to hear it from ourselves. We confronted her over this and she wasnt very apologetic or even seem to care. She has quiet a bad reputation as she is very loud and makes a show of herself on nights out etc but we never get involved and my boyfriend wouldnt be overly close to her, but would be to her young 6 year old daughter. Now i have just found out she is telling people weird lies about me and my boyfriend, one recent one being that me and my boyfriend had loud sex with her and her 6 year old daughter in the house. Which is simply not true as shes never stayed at our house for more then a few hours and we would never be in bed when she is there. I just need some advice as i don't know what to do and this is only one story out of quiet a few. I don't want much to do with her but i don't want my boyfriend feeling like he can't see her and her daughter as he loves his niece so much.