I think his family doesn’t like me!

I have a problem with my boyfriend’s family and can’t seem to be able to get him to understand why I don’t like them. They are polite and don’t say anything about our relationship, but I constantly get the feeling they pretend to welcome me into their home. It’s obvious they want someone better for their son, and I know I am not imagining this because they simply stop speaking or go away when he’s not in the same room with me. I tried having a conversation with him about this, but he laughed it off saying they were just emotionally detached people. Should I tell him that their behaviour is upsetting me and that I don’t want to spend time with them? I am only worried because I don’t want their actions to influence him and damage our relationship.
You are perfectly entitled to your feelings irrespective of what your boyfriend may think. However, he presumably knows his parents better than you do, and is still with you despite what you think his parents believe. You can spend less time with them if this upsets you, because that is a sensible thing to do, but the more important thing to focus on is your relationship with him, and whether that is strong enough. Ultimately, everything else ceases to matter if two people believe they want to be together no matter what.

How do I change some of the things my boyfriend does, without giving him the impression that I want him to change? He is very resistant to this because he thinks I am trying to force my personality onto his, but I am simply trying to make him a better person. What do I do?
If he isn’t a perfect person, going by your definition, why be with him? If he doesn’t want to change something, and has made it clear, you can accept or reject it. Try and remember why you decided to be with him in the first place.