Easy to work out.
If the tables are 7 foot tables. The same distance that is required from the walls is what is required between tables.
I would guess around 5 feet between rails:thumbup:
That's not exactly the right approach. The distance from a wall is determined by the standard length of a cue (add a few inches for good measure). 5 feet is the bare minimum *for a wall*.
Between tables is different because an adjacent table doesn't obstruct a cue. The problem now is stance and walkway. You'd like to avoid someone sitting on one table while shooting on another table. Ideal distance is more than 6 feet but you can probably work with 4 feet of space.
The bottom line is, if a compromise needs to be made, make it between tables and not with a wall. If you want to test this out, go to a poolroom with a measuring tape and place a stool 4 feet from the table. You'll see most players under 6-feet will have no issues but taller patrons will need to bend their knees. Either way, this is still better than using a short cue because a wall is in the way.