Rekeying pattern for duplex with shared front door
See if your particular lock shows up here:

http://www.imlss.com/images/pdf/kwikset_Rekeying_Manual.pdf

Though I think if you have a competent locksmith, you just tell her/him what you want, and it happens, you don't have to tell them how to do their job. And you have an incompetent one, telling them how to do their job is not likely to help, either. So anything past this is merely for information, unless you are planning to try and do this yourself, which can be complicated for boring legal reasons in many LAHJ's rather than technical ones.

I'm not a locksmith (I think we have a few posters that are) but with 5 pins that can be set 6 ways (each) you have many, many key combinations available, and you need, at most, 4 that work together, in 3 lock types.

In some sense you're delving into "sub-master" to get what you want, with each key working specific things - so the unit keys operate the common lock 

52463 Let's say that's the common door.

Now, if you put a master pin of size 2 in position 1 and 4 of the common locks (with bottom pins of size 3 and 4) You can have Unit 1's lock set to 32463 and unit 2's lock set to 52443 and you get what you asked for, with neither being able to open the other via filing down a key.

If you want a full-on master or a front door only key, it's more of the same. Actually I guess I gave you a front-door only key while trying to avoid the "file down to open the neighbor" condition from the comments. If you are hiring a locksmith, they should be able to work out the details without your input on the specifics of the pins used. As such I'm going to stop here for now.