I have the mockingbird and will be converting it to a double stroller this year. The basket is really roomy.
They’re beautiful!
The UppaBaby Vista’s toddler stroller holds up to 50lbs. it has a zillion attachments for all sorts of seating combinations. it’s pricey but super durable. my son is almost five and doesn’t really want to be sitting so I got him an attachment that he can ride on.
You should check out the Zoe Twin stroller! Seems like it’d match your requirements. For the zoo, I prefer a wagon since my 4yr old prefers to hop on and off by herself. But, for normal walks / target runs, Zoe Twin is lighter and easier to set up.