Federal Q2B sirens require big alternators-at least 200 amp back in the day when I was selling fire trucks. The dual battery system is a requirement of motorized fire apparatus by NFPA Standard 1901. The truck must be able to be started off of one battery, which is also part of 1901. As far as the wife on the tailboard, well, that's her decision!
Today, you can get a mini-pumper equipped with a diesel engine-I've seen Fords so equipped. The sad part is that I haven't seen an HO model of a mini-pumper fit for my time period, because I wouldn't mind one for my layout's fire department.