Where are all the recruitable named settlers?

Apparently there are named settlers scattered across the commonwealth that you can recruit. In doing so, if you assign them to a level 3 vendor, it will be upgraded to a level 4 vendor that can sell even better gear.

For example: Ann Hargraves

Who and where are the rest of these named settlers?

Also, how does this affect the stock when you have multiple vendors of the same type?

Small spoilers:

The vault tec rep boosts whatever vendor he's assigned too but not to the level of a level 4 vendor, what happens if I have him and a named settler assigned to the same type of vendor?

The Vault-Tec rep boosts the trading emporium - that is what he should be assigned to. Some of them have unique items to sell which is why it is a good idea to collect them plus they also have better standard equipment.

There is a full list of the T4 vendors and what they should be assigned to here.