no, you can replay them in the mission section of the pause menu
on the storyline there is 51 missions and 18 side missions
you have to play through more missions in story mode.
You can do missions for Bonnie MacFarlane in Red Dead Redemption, that is all.
Side missions are those which are not to do with the main story of Red Dead Redemption. They are usually found randomly across the game but some are marked with a grey or purple question mark during progress through the game.
If you want to be able to do this you need to complete the story missions on Red Dead Redemption and eventually you will unlock the higher levels of dead eye which allow you to use the X's.
you must complete more story mode missions
Do your missions.
do your missions
yes
To get your dead eye level higher you must complete the story mode missions until you are able to get to the next level of dead eye.
No, in undead nightmare you basically kill zombies and do zombie missions
you have to do missions