A side-by-side double stroller puts two seats next to each other. Both children face the same way. The frame is wider than a tandem.
Measure your door first. Then the lift and the path you walk every day. Width is the check that decides this layout.
From birth needs a complete setup on each side that needs it. That may be two carrycots, or the seats the product page names. Do not guess both sides.
Read what the package includes. Then check each seat's limits. A newborn and an older sibling can share this frame only when both seats fit.
If you need a longer, narrower frame, compare tandem double strollers. All two-child frames are in double strollers.