You aren't feeding them anything are you? The cotyledons are looking a bit yellow and maybe burned...even the first true leaves of the smaller ones are looking....not happy. They also look like they might be a bit dry. You do not want them too wet, but it is easy for them to get too dry when they are so little and fragile.
Seeds often pop at different times. The smaller one could end up being just as good as the one that popped first
I do not "pre-germ" the seeds in a glass of water, paper towels or anything like that. There really is no reason to do that if the seeds are not old and dried out and there are some down sides to not planting directly into your medium. Mandala's seed site has a good germination guide that I quite like (I have had no problems using rapid rooters though).
If the source of your random seeds was a bag of weed, then yes you are using bagseed and are chancing hermies. When you get to the flowering stage you will have to be diligent watching them....but that is 6-8 weeks down the road, so not a worry til then.