In order to kill all four bosses before the meeting, you need to have a child, and a lot of firearms skill.
The first boss you can kill is Enzo. You need 60 firearms by the time you turn 37. You have to go in the limo, pull out your gun and begin shooting. In order to actually kill Enzo, you shoot him and the guards, while dodging their attacks. After, shoot him in the head to make sure he’s dead and run away.
Next, when the Don says Taylor/Tyler needs to be killed, you select the option to kill Hiroto. You need $3000 at this point, or the sniper rifle, and 50 firearms. Or just 60 perception.
This is the on where you need the kid. So, you need three police officers or a good relationship with the FBI, and after you have a lot of options to get them to surrender. The easiest ones are using the MAC-11 and having at least 20 firearms, 75 persuasion, 75 subterfuge, or 75 athletics. After, Demetri will apologize, you have to visit him intending to murder him, and you need 40 athletics, 30 firearms, or 40 fighting.
Finally, you have the boss of the Martinez family, Pedro. At this point, you need 100 police rep or 4 bribed officers, 50 streetwise and 90 criminal rep, 30 legal and 30 finance, or 90 Alexis relationship. Then, select the bottom option to shoot Pedro, which needs 70 firearms.
If you wanted, you could become the Boss of Bosses easily after this as long as you have 100 respect.
Edit: If you want to make peace for New Daria, you can’t kill anyone.
Edit 2: Respect caps at 100, and the easiest way to get it max is by killing the bosses. I shouldn’t have said easiest, but it’s the fastest. Don’t get the red convertible, it costs twice as much as the BMW and still only gives +10 respect.