A buggy for two kids   

When my son was born, katt was already 3 and she preferred to walk everywhere. HOwever, when her brother was born , she suddenly decided she would like to go back on the buggy as well.
I looked trough many of the double ones but none fit all my needs. I ended up finding the perfect one in a second hand store just for kids. There was enough space for him to lay down in the back part, and enough for her to sit at the front. It was a bit long but very easy to maneuver.
I was just checking the ones that you mention and they look good, but like you I am a bit wondering where I would put the little baby. Mine was not as streamlined or modern, but had a surprising comfy area for the small baby at the back and a pretty nice one for the toddler in the front.
Is there any specific part of it that actually will go flat, for laying down the baby?

I have both types of double strollers. My side-by-side stroller is a jogging stroller that is meant to go on all kinds of terrain. It works well for the trails I jog on and other outdoor adventures. However, it is too wide and bulky for stores and other public outings.

I have the one in front of the other kind for the stores and public places. My son is only a month old and I love the stroller as it allows the car seat to be attached to the stroller. He is too little to sit in a seat so he can easily stay in his car seat. There are two seats so when he is older and able to sit on his own, he can use it. I recommend it and think you should look into this type of stroller.