The DB4 is a very good UHF antenna but it's not intended to function well in the VHF band. Real channel 10 will be received more reliably if you add a high-VHF antenna such as the
Antennacraft Y5713. You would need a
UVSJ to combine the signals from the UHF and VHF antennas into a common down-lead.
I'll recommend against the AP8800 in your case. The AP8800 is a 'fringe' or 'deep fringe' amplifier. It is designed for locations with weak signal levels. The strong signals in your area are likely going to overload an amplifier of this type.
I don't believe you will need an amplifier to drive four sets, but a high input amplifier can be added later if it proves necessary. Pre-amplifiers such as the Antennas Direct CPA-19 and Winegard HDP-269, or distribution amplifiers such as the Channel Master CM-3410 and CM-3414 would be viable options.