Ooo it certainly brings a new perspective to motherhood. Having coped with the fears of preeclampsia, threatened miscarriage, long nights in A&E, bullying and the threat of permanent disability- I am now Haunted by the fear of the Prospective Daughter-in-Law.
-Oh, mrs Cory, I am so happy to be meeting you at last, Coryboy has talked so much about I feel I know you already, will you show me the pictures of him as a baby, oh and will you just tell me how you feel your menopause is affecting your mental health...help, help, help, POLIIIICE...
It did not occur to you, Xenia, that people have different registers and what is interesting conversation in the close family circle becomes downright impertinence when addressed to comparative strangers. Adressing people as if you were their psychiatrist when they have not asked you to do so is unbelievably rude. Particularly if done by a younger person to an older.
I also have a fair proportion of psychiatrists in my extended family, but they keep a different set of conversational topics for their social life.
My children frequently and light-heartedly call me fat, but the day they say the same to the deputy head I shall run away to the Continent under an assumed name. The difference between private and public register is one that I would expect a child to have mastered by the time they are six.
Good manners are about adapting to what other people find interesting- particularly if you are a young girl coming into your boyfriend's family. Instead you are encouraging her to criticise his background and (in consequence) his upbringing- sounds like you are doing your best to mess up her private life. It is not for you to decide whether this relationship becomes serious- but if it does then her loyalty will belong to him not to you. Nothing wrecks domestic happiness so quickly as the MIL ganging up with her offspring to discuss the other side.