Try not to be confrontational, as that will defeat the point of the conversation and will likely make your in-laws feel defensive. If this happens, they may continue to act in the same inappropriate manner. When disagreeing with your mother-in-law, consider saying, “Is it possible, Mom…?” (Halachically, this is the correct way to speak.) Something else you might say: “We always enjoyed a close and caring relationship. I was hurt about the situations that occurred. Is something deeper bothering you? These situations never happened before and I want to understand them. They are unlike what would have taken place in our previous relationship. I want to go back to our old relationship.”
Since you seem to portray your in-laws as typically having a good relationship with you, they will likely understand and apologize to you as well. It is a shame to let a good relationship go sour over several misunderstandings. If you can be the bigger person, hopefully this rift will be repaired and you will feel some validation in the process. This will be difficult to do, but you will gain much more in the long run.
I do not know if you might have inadvertently done something to hurt your mother-in-law that she is not telling you about, but is instead acting out her frustration over this – to your detriment. If this is the case, she will hopefully feel better after you demonstrate to her during the course of your conversation that you care about her. The fact that you shared a good relationship prior to these two situations bodes well for the healing of your relationship.
Remember to use the “I feel” message and to speak in a soft tone. If you feel that you can’t do this alone, seek assistance from a competent therapist or rav. Hatzlachah!
