Why the resistors needs higher Ampers if the Total current is 4 Ampers?
You've already calculated the parallel resistance of R1 and R2, put those in series with R3, and calculated the total current correctly. 

Now to finish off, you need to use the correct voltage drop for each series resistor. Using Ohm's Law the other way round, the voltage drop is given by \$V=IR\$

For: R3, \$12\Omega\$ * 4A = 48v
For: R1 || R2,  \$4\Omega\$ * 4A = 16v

Together, the 16v and 48v add up to 64v, the total input to your circuit.

In an entirely series circuit, one in which the current is constant throughout, the voltage across each component is proportional to the resistance of that component.