congrats mama!
we just sold our triple jogger a few months ago. it was a Baby Jogger Q series. i dont' think they make them anymore, but we found ours on CL in colorado. it has 4 wheels, fixed in the front. has the usual BJ fold and it is WIDE. (but did fit in the back of our suburban). i'm not sure you would like it push wise, as fixed front wheels = harder to turn when walking but for running with that many little ones, its great.
with the terrible sidewalks, the triple jogger would likely be too wide. dh would run with it on the side of the road (not busy, more like neighborhood streets).
maybe a valco tri mode EX twin?
http://www.valcobaby.com/products/st...e-ex-twin.html it comes with an optional 3rd seat.
and get your oldest a balance bike. by the time ds was 3, he could maneuver the balance bike really well on our trail, so i just had to push a double.
also, for getting exercise, a baby carrier + double stroller is a great option. and a bike/seat/trailer will give you a good workout. our trailer has a nice sling that reclines a bit. and you can get a good infant insert. i started with dd in it at about 6 months, on the trail. (its soft surface, bike/runners only, flat and low speed, so i'm fine with it). the trailer is a smoother ride then the jogging stroller was.