ADD: Based on the new info, I would talk to the school counselor. Ask her about strategies to help him or talk to him. He may be desparate for a safe place or affection or something, which is sad. A comment like "left handed people are evil" isn't socially clueless, it is weird, besides being wrong and mean.
Based on his parent's behavior, try to put yourself in his shoes a bit - if he is only 5 or 6, he's in a bad place and needs understanding. If the counselor can help with this, getting a different reaction from adults, instead of being creeped out might be helpful. Kids aren't stupid, so if his parents aren't teaching him the why's, perhaps others can help - not in a lecturing way, but in a caring way. Don't just tell him what to do, give him the why - and ask how he would feel if (my son really gets things when we give him full picture + "how would you feel/how do you think they feel" back-up instructions).
ORIGINAL: WHY do you think his parents are wierd? What are the other issues not mentioned here?
What you are describing doesn't send up red flags for me (and I have personal experience that makes me more sensitive to red flag issues). Nothing you describe is sexual at all. Boundary clueless, yes, but not sexual.
My first thought was autism spectrum because of not respecting boundaries and sensory seeking. If he and his parents are all on the spectrum, which is possible as it has a genetic component, they would seem "weird" to others because their speech pattern, body language, eye contact, and other things are not typical. Put that together with boundary issues (social challenges) and sensory seeking and it's a big social mess for him.
Your mama gut may be feeling that weirdness, but if you have other info that might give a clearer picture, just "ADD" that to your question at the end :)