ive never grown pot, but veggies like the tomatoe plants i grow each summer did not do well when seeds were in the same contained medium. the bigger seedling would leech/hord all the water and nutes from the smaller. If you cant get another container, at least use some sort of plastic as a barrier. Hell even a shopping bag, somethig to keep the bigger seedling from starving the smaller. But get another seedling disc/pot, really, or a plastic cup, or bag filled with dirt or anything. Improvisation is the key to success in my mind. hell grabbing some wet dirt, balling it up in ur hands, and putting it on the ground with a seedling in it would work better than two seeds in one pot. Have u ever seen what happens with "two girls, one cup" ? trust me its not pretty