HELP!!! Double stroller option?

Kathleen • My name is Kat & this is my 2nd pregnancy due 07/04/2016! I'm married and have a 3-year-old son plus 2 French Bulldogs.
I am due in July with my 2nd baby boy. My first born is 3 and will turn 4 in September. I have a couple of questions...
Would I need a double stroller?
Do 4-year-old's even need it?
What options can I choose from?
(I'd recommend tandem vs side by side)
Thanks in advance!