What do you do when you already don't like him?

My 24 year old sister is dating this 33 year old man that lives 700 miles away from her. They have been dating for about 5 months or so now. He is coming into town this week to meet the family. My sister has met him in person about 4 or 5 times now, when she drove to his state. From what my sister has told me about him, I already am not fond of him... She has told me that he lives with his parents along with his 2 kids from a previous relationship, he works part-time only and does not want to work more than that. In his free time he likes to play video games, do drugs, watch tv, and hack things online. He does not have a car or a drivers license. She claims to love him so much that she is thinking they it is about time that they combine their lives together by him moving here or her moving there and starting life anew.

So my question to you is this: What would you do in my situation? Would you fake nice all the way while you're in person with him? Would you tell your sister what you actually think of him?

Any reasonable advice would be great. Thanks.