no.. that doesn't look okay, lol.
they will definitely compete and most likely 1 will dominate more often than equal sharing.
even the non-dark seedling is looking rough. Definitely some sort of imbalance in your water. If it's too cold at night, might be why the one turned oddly dark and maybe other is abit more resiient in that 1 way but you already have visible symptoms in leaves... something is drastically off for that to happen this soon.