As someone who comes from the same place as your inlaws (but respect what the mother's choice is in the birth of her child) if you care what they think I would try to alleviate their concerns.
I have seen BOBB (and maybe you could have them watch it). I think my biggest concern would be, and maybe for your inlaws as well, is what happens if something goes wrong (baby gets stuck, isn't breathing, etc.). For me, I will always have a hopsital birth because every second that child isn't getting the life helping care that he/she will need may impact their quality of life. This includes the time to call an ambulance, the time to get the ER etc. This is my biggest concern about home births.
Once again the information only applies if you care what the ILs think, but if you do then: 1. tell them you why you want a home birth (more choice, more control, better following of birth plan, more natural, etc.). 2. Tell them your game plan in case the unexpected happens. 3. Answer questions that they are going to have but limit it (I will answer questions, but at this point I'm unwillingly to listen to any negative support about my decision).