This is basically what's thought to have happened with proto-Earth and Theia in one of the main Moon-creation hypotheses.
Main planet forms, creating a gravity well. Smaller clump forms at a Lagrange point of that gravity well. Then it gathers too much material or something else causes a destabilisation of the Lagrange point, causing the smaller, possibly now well-formed clump, to fall towards the Lagrange centre, i.e. the main planet.
In Earth's case, the clump was Theia and the resulting collision exchanged material and ultimately spat out the Earth and the Moon.
Maybe the same will happen in this burgeoning system, but we might be waiting a while to see.
pgetsos