No lah..try my best..some fish can differenciate (Eg. scooter blennies, clownfish, pipefish). Jawfish virtually impossible (Just hope for 50% chance). Gobies I'm not sure...for my black fin goby I know the female is the larger one while the smaller one is the male..cause mainly sparing occurs between males...for the yashia I dunno...I just picked very different looking ones..
Anyway..gobies not very aggressive. Even if both male nvm..as long as your tank got space for them to have their own space.