Scissors, WHO put this thought in your head?
Am I being really over sensitive?!
Because NO, you are not.
If an adult treated my dog the way these fuckwits are treating your boy, they would get one short, sharp rebuke & a chance to redeem themselves. They would never be left unsupervised around my dog, & if they fucked up again like that, they'd not be welcome around him ever again.
They are teaching your tiny boy that adults are not to be trusted, that hitting is funny & gets attention, that lying is normal, & that he has to tolerate being wound up.
Are you going to let this escalate, or are you going to get angry with whoever or whatever made you doubt yourself with this too sensitive nonsense, & use that anger to protect your son?
How is DP handling it? Are these his relatives? Is he going to present a united front with you to get the relatives to quit their bullshit?
Apologies if this is coming over as harsh, I'm not looking to upset you, just angry at your fuckwits. I know each individual incident can be written off by the relatives (& maybe DP???) as "just teasing" etc - but cumulatively, they are adding up to teach DS all the bad things I mentioned above.
I lived with a family member who behaved similarly, & it wrecked my young self-esteem. Children need stability, confidence, consistency, & faith in the words & actions of their close adults. Don't let these relatives mess with that.