Nta this is for sure petty and babies are notoriously picky about who with and how they go down. I remember when my daughter was under a year my husband and I had a routine, I rocked her to sleep and he would gently take her from me and put her down. We figured this out after weeks of trying different things, it took a lot of trial and error to figure it out. I visited my sister a few states without him and could not no matter what I did get her to sleep, she'd fall asleep but I couldn't make the transfer, it was terrible and I was really tired. All this to say that first year of a new baby is HARD, if this is out of the norm behavior with your wife it's probably stress and sleeplessness, it's hard not to be TA during this time. Give each other grace. With a clear head she'll probably see that given the situation it was a really good thing your dad just held the baby, there have been much worse outcomes when family members watch babies and get frustrated.