If you're asking that question, maybe you shouldn't be doing the job.
I think it was Clint Eastwood who said it best - "A man's got to know
hos limitations.'

I have been asked to photograph the families of my church parish for a

You want a weeks worth portrait workshop training in a usenet post?
The good news is that you are bound to be better than 99% of the
church directory shooters out there, whenever I see some god awful
example of clueless lighting and graceless posing its a church photog,
so by asking at least you show some hope of stepping up.

Its not a matter of simply different heights, people are different
heights and a group arrangement tends to be better when the heads are
placed in compositionally appropriate positions.

The classic is the pyramid.     Dad (typically the alpha) at the peak.
Even if dad is some wilty milk toast and mom is a mountainous weight
lifter six inches taller social convention expects him to be Mr
Familyman at the top of the heap.

                    dad
                       mom
                kid
                     baby
                           kid
             kid

Ideally you don't want any two heads on the same level.  Certainly not
two heads of the same level NEXT to each other.

For close ups of the parents, kids together etc, the taller one's
mouth is usually at the level of the second's eyes.

Ideally you want everybody the same distance from the camera.  I know
several photogs that will string from the tripod to the forehead of
each person in a group.  string is pulled out to the first posed
person's forehead and pinched, then when he poses the next he holds
the string out and has the person skooch or lean closer.  This
prevents distortions in head size, especially when some of these goofs
are using a zoom lens at less than telephoto position, then they have
a kid in back between the folks, and a line of kids in front and the
babies and toddlers on the laps, four deep and you can see that the
ones in front have heads a quarter or more larger than the kid in
back.

adjustable stools are great cause they allow you to possition the seat
height for the height of the person, an inch or two difference makes a
major difference in how the body fits, most of the time the seat is a
bit to high, we are used to that so we don't really notice it, put
someone in a seat too low and you see how they don't look right, (just
came from a neighborhood meeting at the local elementary school...)
bad seat height hurts far more than good seat height can help, but its
the best place to start.

go find some scrap lumber, two by wide, wider, widest.  you will need
some chunks to place stools on, or feet on, or butts on cause you want
to position two things, each person for themselves, then each person
in relation to the ones next to them.   If things get confusing, in a
group shot the more important thing is how each person position
relates to the others.   phone books, planks, catalogs, and for Mr and
Mrs Jack Sprat, a huge soup pot might come in handy.

Place the first folks at 45' angle to the camera, especially mom and
dad.   I usually 'prom' pose them or spoon them, mom in front of dad,
baby on her lap, toddler on dad'd knee between him and ma, older kid
perhaps standing by dad with hand on his arm.  the kids I try to pose
45' the other way.

babies, you will probably have lots of them. (and churchy families
tend to have lots of them and they are radioactive, like heavy metals,
close proximity of a 2 and a 3 quickly hits critical mass, and never
EVER agree to photographing a 3 yo's birthday...)

hold your hand out, palm up and thumb out. place the babies bottom
there with the thumb between the legs.  the other hand grabs the
clothing between the shoulder blades, I try to get the mom to use her
three lower fingers while the thumb and forefinger cradle the infants
neck.  She now has full control of the child, can tilt him up without
fear of dropping him, and without horrid hunches in her back and
shoulders.  NO more Quassimodo mommies, please.

Now that we've cleared that all up, please tell me that you will NOT
place your umbrellas on either side of the camera like it seems they
oughta be, please, (all the regulars on this list are now reaching for
their delete or next button cause they fear I'll dredge up my usual
sermon from my cultish Temple of the One True Light)

This message is echoed to the z-prophoto mailing list at yahoogroups
where you might find a lot of help in the archives...

Sam,
Maybe don't try to reinvent he wheel here and do your shots outside like
the ones on your web site. Is that possible? Some open shade near the
church would probably be much nicer anyway, weather permiting. Couldn't
be worse than the average church directory lighting.
Jack