Issue seems to be solved.
I finally got time to dig into this again. My son was able to tell that the noise was definitely coming from the front brakes, and only during the very last few feet of braking. It was happening on just about every stop, but got worse the hotter the brakes would get.
Pulled front hubs and using a file, l put a more pronounced angle on the leading shoe lining.
Basically held file vertical and worked back and forth along edge of material. There was a slight angle there to begin with but I filed until I had maybe a 1/4 inch wide band across the shoes that angled down through maybe half the thickness of the lining. Also did same to edge of the “back” shoes.
I cleaned the drums and also added a little more brake grease on the contact areas on all shoes.
I also noted one side the springs sort of “interlaced” and crossed over each other on the pin, so I re-set those springs on to the pin so one was cleanly on top of the other. Not sure if that could have been a factor but it didn’t seem right how I had done it initially.
Reinstalled hubs and wheels and then adjusted all 4 brakes. Also adjusted hand brake cable.
Wow, what a big difference! Stops are nice and crisp with zero squeaking. Pedal is firm and less effort required.
Thanks to everyone who offered all of your help and advice!