Emotional harassment from in laws

I am a woman married in a good household. My husband is very supportive and is not biased. My MIL has problems with me origin of which m not aware. She is a cunning shrewd liar who always works at getting out of a situation by hook or by crook. She always ALWAYS taunts me over anything and everything that happens. I am a working woman who can’t leave the job even if I have a 3.5 yrs old kid. My son was s looked after by my in laws and they diligently look after his well being that I don’t doubt about. For the first two years I never fought back or reciprocated to their taunts or fights so much so that my husband used to scold me for not opening my mouth. But once or twice they commented on my parents and that was the end of it I started fighting back verbally because fours years worth of frustration is pent up. Recent fights happened twice in these fifteen days wen my father in law was out of town So now they have very cryptically threatened that they are approaching the police. They have not said that this this is due these fights but I want to be prepared in case they are planning to do so. Please help