As for the twins, I recommend letting them grow naturally and see how they develop. It can be disruptive to try to separate them, very easy to cause damage. In my experience usually one ends up dwarfed and eventually looks like a lower branch of the larger plant that forks out at the soil line.
Certainly no need to cull any of the twins. As you go into flowering, just keep an eye on any dwarfed twins hiding in the undergrowth to make sure they are stable.
If you want to try to keep them equal sized, do some gentle training and just bend their stems apart every day. Sometimes you can get a nice looking v-shaped pair of plants that way.
I’ve also gotten some interesting twins in my f2’s of bodhi’s work: