I feel you. My in law's family is also very loud as my fil is partially deaf so he talked v loud as though he is scolding someone. The TV volume can be so loud that the neighbour came over to feedback.
I had the same problem last time and it happened when they came over more often when my baby was 3 mths. Baby was startled at the loud voices and cried non stop. They said to let her get used to the loud noise and to familiar her to their voices too. Things didn't go right as my gal would get startled and cry even at night. I spoke to my husband and he noticed the trend.
It was then, that my hub spoke to his beloved parents and how difficult we had, to handle baby at night. In law began to mellow down and tried to talk softer. Things got better and we were thankful that our in law's didn't overreact.
Communication is very important. Try talking and letting them help you.
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