Have a question for someone with electrical knowledge. I have a 12 volt electronic circuit board the has 2 fuse holders for each circuit. Directions say 1 fuse will work but you can double the capacity by using 2 fuses, { 2 -25 amps fuses will handle a 50 amp draw. ] My question is , why wouldn't the first 25 amp fuse blow and then the other leaving the circuit dead?

because there in parallel so there drawing through both at the same time. so you won't be pulling pretty much 1/2the draw through each.

Electron flow is like any liquid flowing, they all take the path of least resistance
In direct current circuit resisters(fuses also) in parallel reduce the total resistance by 1/2, hence the advice on using two 25 amp fuses in parallel instead of one 50 amp fuse
In a series circuit it increases the total resistance making the two 25 amp fuse become like a 12 amp fuse
I made up a demonstration example of this using 25 watt light bulbs in series in and then rewiring them in parallel for my Son years ago when he was in junior high school, he didn't get the theory right away but he saw and understood the working example right away
He had a friend who was trying to wire a older VW bug up for a big sound system and he was trying to get by cheaply by using small gauge speaker wire and wire the speakers in series