now for the 2 pinball buttons, do you just plug them into any regular button port? so they will work, but the button that is also in that port will work it to?
this may sound confusing so im sorry.
Sounds like you want a total of 2 flipper buttons.
I use a total of 4 to support the greatest number of tables:
1. Left flipper
2. Right flipper
3. Left upper flipper/MagnaSave
4. Right upper flipper/MagnaSave
(search using my username and "MagnaSave" for posts on the finer points of configuration and wiring for MAME+Pinball setups)
You can wire the left pinball flipper (left shift) in parallel with Player 1 Button 4.
For the right pinball flipper (right shift) you can either use a dedicated IPac input or if you don't have enough, reprogram a player button to right shift and reconfigure MAME -- MAME is easier to reconfigure than Visual/Future Pinball.
As for your question about ground, just remember that "ground is ground".
The purpose of the button switches is just to apply ground to the input.
Nothing wrong with having the daisy chain grounded at both ends, but it's not necessary.
The advantage to having both ends grounded is that if both wires pull out of one QD in your ground chain, that is the only switch that will stop working.
Like Khalid74 says, make sure that your crimps are secure.
I prefer using pre-fab daisy chains for this reason. YMMV.
Scott