Its been a few years since I traveled with infants. It is my understanding that you were assigned these 'preferred' seats because you have a infant and these seats are where you can attach a bassinet to the bulkhead. Yes you lose seat width because you cannot move the arm rests and you have to stow your bags during takeoff and landing. The benefit is that the infant will be in the bassinet and the remaining three of you will be seated together plus you have legroom. This is likely the best option for you unless you prefer to carry your infant for the entire flight.
Hopefully other FTs experts will also weigh in with their suggestions.