Twins?

It is time now to plant the seedling, plug and all. Once the root is protruding, it needs to have access to somewhere to continue growing. Normally with "twin" seedlings, there is only one tap root as both sprouts emerge from the same seed/embryo. I would suggest cutting the smaller twin off, leaving about an inch or so of stem remaining, this will dry out and wither away in time. If you cut it off at ground level, this could cause/provide a great spot for fungal attack. Having had a few "twins" in the past, getting rid of one is the only real option, otherwise they will compete for food, light, root space etc and instead of getting 2 plants, you end up with 2 half sized plants due to them competing for everything. Hope this helps,... Organoman.

You don't normally take them out of the cube ever. You plant the cube and seedling together in your soil or hydro medium. I would pluck the small one right where it meets the surface. Any leftover green should die off and the shared taproot should focus on the remaining one. Trying to save them both could just result in two very stunted plants.

Those are indeed twins! it's one amazing mutation that isn't too rare with cannabis! I'd suggest removing the smaller one to prevent them from fighting for root growth space, and nutrients! You can even replant the smaller one and grow it as well! Good luck and happy growing :)