I assume the white 'string' like things in the picture are roots? They are coming from all levels of the plants, even in the middle. Should I be trimming the roots that are above the substrate, or just let them all grow?
They don't seem to have any roots at the bottom of the plants. So they easily become uprooted and start floating around. I was thinking to solve that problem, to prune the plant to just below the first set of roots and then to put those roots under the gravel? Would that work? Or should I just let them be? They are growing fine, I just don't want to have to replant once a week during my water changes.

They don't seem to have any roots at the bottom of the plants. So they easily become uprooted and start floating around. I was thinking to solve that problem, to prune the plant to just below the first set of roots and then to put those roots under the gravel? Would that work? Or should I just let them be? They are growing fine, I just don't want to have to replant once a week during my water changes.
