Oh Charaz that is just terrible babe.
I would change his name to one that you want, He is your son not theirs and if they don't like it tell your FIL to get MIL up the duff so she can name HER baby after him. They will get over it and if they don't then the grief is theirs not yours. I have told a similar story in here a while ago, where I was nursing a lady and her Overbearing MIL was exactly the same, I really felt for her.
Now you said bub is two months old, is he a June baby? If he is I would like to invite you to join the June Babies thread. If not don't dispair there is also a May one you can join in on. Welcome to Belly Belly, WE would live to hear some details about your pregnancy and Birthas well as all the stats on bub. Feel free to vent and share your feeling, everyione here is great and very supportive. Chin up, the sun always rises on a new day.
Bye Dee