Hi, first of all I also use jiffy pellets with big success. Lately I was having a twin seedling, they both unfortunately died. If the first plant is doing OK then what the experts recommend, cover this other "stem" with soil and see if it springs upwards or nothing changes. Chance is, the twin is already dead. But if not, and you will manage to separate them (before their roots entangle) then one plant is an EXACT copy of their mother and second is a mixture between father and mother. Good luck and let us know!