Is this a red flag? Should I ask my bfs sister?

So my bfs sister is older than me by a couple of years. Well few years ago she borrowed a car from a family friend. This car was a brand new car at the time it was a 2014 year car. She borrowed it for a week just for fun. But then we I met the family friend it was a middle age man who I then found out has always been single. Anyway, my bf then told me that this guy knew his family since they were like babies. But he said that this guy never bought presents for anyone but his sister since his sister was like 8 years old. My bf has three siblings so I thought it was odd. My bf said he would only ask about his sister and he said maybe because she's a girl. But I kept thinking that it was creepy but didn't say anything. Well few months later she borrowed his car again. I thought that well maybe he likes her I mean who else would let someone borrow their car for fun? That's not the issue though. I got a new car and I gave my bfs sister a ride and when she went into my car the first thing she said was " eww this new car smell reminds me of that guys car!" And she kinda like shivered and rubbed her hands across her arms when she said it. I thought it was strange for her to say that as soon as she goes into my car since I don't even know him that well. But thought it was also strange that she said eww? Last time he was at her house I saw him peeking when she bend over for a long time. It was gross. I get now that she's and adult. But her parents don't care! It's obvious he likes her and her parents are okay with it. Isn't this strange? I wanted to ask her if she's okay? But I thought maybe I'm just looking into things too deep. My bf thinks all his parents friends are creeps except for that guy. But that guy is the biggest creep of all! I've witnessed other things but just thought I'd share a few examples. Should I tell my bf about what ithink about the guy? My bf and I have been together for several years and we are in love. What if we have a child together soon and I tell him all of a sudden I dontwant my kids in his parents house because their friends are creepers lol would it be best to just tell him now? 😓 I also worry about his sister? Seems odd. I don't want to assume but his parents are the kind of people who wouldn't care if an old guy is trying to pursue a child.