The vines that I'm looking into produce black grapes.
This link https://homeguides.sfgate.com/tall-can-grape-vines-grow-65427.html gives some guidance regarding planting, as well as training and pruning. The usual advice is to plant 6-9 feet apart in rows 8-12 feet apart, but you're growing them on a pergola (or arbour) so that doesn't really apply. You will note from the link that a vine grown on a pergola will need 75-100 square feet of space to thrive - I'll leave you to do the math on that!
I do have strong reservations about how successful digging up those vines and trying to replant them will be; it sounds as if they've been in situ for some years, so the root systems will be pretty large, and root damage is inevitable, to the point it's likely to be fatal. I'd recommend working out how many vines you can accommodate (I still think probably two at most, but really there's only enough space for one mature vine on your pergola) and buying what you need and planting new.
I would plant two grape vines.
Vines can growth large, one is also enough
I prefer two to have a back up (especially if you plant very small vines
With such small surface, you do no need professional plantation (see as: minimizing overall costs [easy pruning without ladder, easy to use machines [grass, harvest, antiparassitic, etc.).
They should not have much competition (between nearby, for roots and sun). The problem with larger (and few) plants: one could prevail. But with few plants and space this should not be a big problem (and you can see the problem and prune more).
Lifetime. This is a problematic point. Actual grafted plants do not have a very long life. I do not think this is a problem on pergolas, and if one die, you may replace it. The other one could also be a temporary substitute for the shadow. Additionally I assume you are looking for grapes to eat: such varieties may have less that problem (e.g. often not grafted: there are good vine grapes which are not Vitis vinifera. Not so good to wine [a foxy taste], but often preferred varieties to eat) )
But i would also check how you will do the pergola (the structure). Often symmetry is better (visually) than the optimal number. To 5-6 (maybe also 9) could be manageable. Pruning would be more difficult, and with more than 2 or 3 plants, I would in any case use only one variety.