Ok, here is how I would proceed.
Is the middle trunk bent and hardened so badly that it cannot be straightened up again with slow training and patience? If so, then I'd trim the grape vine back to just one main trunk next spring (one of the side branches that is still semi-flexible) and start with that as my main central leader, while selecting three nice branches on each side of the chosen branch at three different levels to use for main scaffolds. Then I'd follow standard pruning instructions for a three tiered espalier from that point forward. In the meantime, take the branch you are expecting to use and tie it upright to a stake asap so it will be easier to work with next year and won't harden into a kinked trunk shape like the other one.
If you think that central leader CAN be fixed, then do what you can with it this summer and fall. You might tie the bent section to a stout straight piece of branch, and then attempt over the next few months to slowly bend it up into a straighter profile using the stout branch as a splint. Then next spring use the two side trunks as your first tier of espaliered scaffolding branches and select two more nice ones on each side of the central trunk for the upper level scaffolds, prune the rest back, and press on. In the meantime, tie the whole thing to a stake and a low cross wire with the main trunk in the middle as straight as you can make it without breaking it, and stretch the two other leaders out to the side as straight as you can so they don't become unmanageable or break in the interim.
If this isn't clear, I can try to draw you something to illustrate.
Edited to add: Another option for this vine might be to grow it as a fan-shaped espalier. You would still have the issue of what to do with that bent central trunk, but it would be less critical to the overall success of the espalier-ation than it would be if you did a strict three-tier vertical system.