No two seeds will be exactly the same phenotype or have the same "robustness" as every other seed, even from the same exact mother and father. You don't really have a problem at this stage...if they continue to dwarf, you can still grow them out and they will produce some bud, but they will prolly never catch the two more robust growing plants. If you clone, don't bother cloning from the dwarfs, just take cuttings from the bigger plants. Your other option if space is an issue is to waste the dwarfs, and pop some more beans!