Hi there @Ad Lib,
Just thought I would check to see how your first week or so of 2017 has been - Happy New Year should be about new beginnings and I hope that the relationship between your in-laws and your own family (i.e. hubby and your 2 little girls) is one that is improving but more importantly less of a focus for you.
I agree with the other ladies that a bc diagnosis is not easy for anybody and other people's reactions are so unpredictable. The way that I have built some resilience is by a new mantra - "Please don't make your problems, my problems".
Love the idea about writing a good old fashioned letter just like @TonyaM suggested. Social media can sometimes not feel as though it is so "personalised" and perhaps your in-laws don't use it or would prefer correspondence "the old fashioned way".
Ultimately, your husband will need the support from his family so he is better able to support your family. He will need a good sounding board and as you said his sisters' husband is an oncologist - there should be some level of understanding here. What is your husband's relationship like with his brother-in-law ? Perhaps he could have a chat with him - both in a personal and professional capacity.
I have many a great story about my bc diagnosis and my in-laws - during chemo my mother-in-law commented to me "I will feel better when your eyebrows grow back ! " and also my brother-in-law who had a newborn asked if I would be a danger to his newborn son as I might be toxic from the chemotherapy ! Oh yes, these things stick and are very hard to forget.
I totally get where you are coming from - I was in my mid-30's when I was diagnosed and had a 5 & 2 year old. Your focus needs to be on your health, your husband and children.
My very best wishes to you and your family.
Sheryl xx