A.L.
For my daughter we used a Enflow infant seat, and for my son, the Graco Snugride. I really like the Graco. It is easy to snap in and out. Stroller wise, I have a stroller that the Graco infant seat snaps into. It is not Graco brand, but it is made to fit Graco (I got it at Target). Anyway, this made life so much easier while my son was at the stage where you take the whole infant seat out with baby in it (those things get heavy quickly). I wish that I had had it when my daughter was an infant. Target also has one that is made by the same people as mine called the sit and snap- I think. It allows a place for one child to either sit or stand and a place to snap in the infant seat. Now that he sits on his own, we use an umbrella stroller. It takes up much less space than other type of stollers and is less complicated to fold and unfold. Umbrella strollers and other strollers are hard to use with a little infant unless they have a 5 point harness. The type that snap at the waist only are fine once they learn to support themselves, but before that they need the shoulder straps to help support their upper bodies. (Another reason that the strollers that the infant carrier snaps into is great- plus if they are sleeping, you don't wake them for the transfer).
As far as having two young ones, I'm trying to work that out myself. There are 3 years between my son and daughter, so that wasn't an issue, however there will slightly less than a year and a half between my son and the baby I am carring now.
Congrats and Good Luck!!