2007 Hyundai Tiburon Gs Manual Transmission not cranking

Hi there so I am helping a friend diagnose his no start condition on his car.
When I showed up he had already bought a new starter and had me replace it
for him just incase it would be that. After replacing charged up his battery and
while hooked on he tried cranking his car and it just clicked. I turn his
headlights on and try cranking the vehicle but it continuously clicks and does
not crank and lights dim out. I thought it might be bad connections to the
battery or a bad ground but I cleaned everything up and made sure terminals
were good to make a good connection so I know its not a battery issue. His
battery did test as having a bad cell, but regardless I put my new Gold Duralast
Battery from my Toyota Camry into his car and tried cranking it but again it
would just click. I notice that the crank sensor does sense the vehicle is trying
to crank and the rpms and mph kind of fluctuate a tiny bit as if it was reading
like the vehicle is trying to crank. connection to the new solenoid is good and
everything was put correctly. My cousin in law told me that there is a plug that
can be undone to manually move the flywheel with a flat head screwdriver to
make sure its not stuck or engine is locked. Where is this bolt located and
what does it look like? And what would cause the flywheel to stick?
Also, I couldn't find that bolt or plug to move the flywheel so I decided to put a
cheater bar on the crankbolt and turn it manually clockwise. I did not see the
crank pulley rotate at all and I did not see the accessory belt moving at all
either. Are they supposed to move when I turn the crankbolt with my cheater
bar or no? My cheater bar turns but not the pulley or belt that goes around it
which is weird. What does this mean?
Also, maybe I'm overlooking things but it could be that my brand new battery
was NOT strong enough to turn his vehicle and start it and that he needs one
recommended for his vehicle?
Oh I should also point out that we tried push starting it several times properly
and it did not turn over???? How?? Whats causes this to happen. We for sure
did this correctly.
Just wondering what to check for next or if I am doing something wrong or
what not. Any help would be greatly appreciated. Thank you!