This is my fish, today I noticed that they’re tail had split all over, I can’t find anything online that looks similar to this. Please help!

What could this be and how could I treat it? They have two tank mates- neither of them bully them and I’ve never see them harass them or bite at their tail.

Is this the early stages of finrot? and what can I do to save my fish and they’re tank mates. Also I can’t remove my fish to stop the others from getting sick unfortunately.