I agree with Diogenes.
Your problem isn’t with your in-laws. Your problem is with your husband for not tearing strips off them for being so disrespectful to his wife. His parents do not have to LIKE his choice in partners, but they do have to respect it. To do this in front of your children is just compounding the issue greatly. Is your husband furious with his parents for behaving that way towards you? Is he refusing to let his parents do further damage to you and his children? Or is he sighing and saying “that’s just how they are” and trying to get things to ‘die down and go back to normal again’?
Chotii, an apology that has to be asked for is worthless. You say this cycle of insult/bad behaviour followed by the “it’s in the past” brush-off is continuous. You can’t change your in-laws. You CAN change how you react to them. Best results will be accomplished if you and your husband sit down and discuss their behaviour, the consequences, your boundaries, etc together, then enforce them. If your husband will not get on-board however, I would suggest changing the way you react to them.
You may also find some helpful advice on in-law relations here.

If that doesn’t work, consider refusing to be left alone with them, so they have to say their nastiness in front of your husband, who can immediately back you up. Good luck 