Is this normal? Need some help, Thanks!

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SOIL GROW

Strain - White Russian, Afghan Kush Special
# of Plants - 5
Grow Type - Soil
Grow Stage - Vegetative
Bucket Size - 3 1/2 Gallon
Lights - (1) 400 Watt MH
Nutrients - General Hydronponics
Medium - 75% Ocean Forest 25% Perlite
PPM - N/A
PH - N/A
RH - N/A
Room Temperature -78 to 84
Solution Temperature - N/A
Room Square Footage - N/A
Pests - None Known
I have 3 White Russian, 1 Amnesia Haze Auto, 1 Afghan Kush Special
The Afghan Kush is the one in the wheelchair.

Okay those are the stats. So now the problem. I planted the seeds 12 days ago and three (White Russian, White Russian, Amnesia Haze) of them are growing great. No worries. But two ( White Russian, Afghan Kush) seem to really be struggling. The Afghan Kush can barely stay up on it's own without support and the White Russian is only slightly better. I have a fan running to help with strength as well. I come in sometimes and they are completely laying down. Their roots don't seem to have branched out very far either as I can barely dig and see where they end. Am I doing something wrong? Should I just pull them? This is my first grow so I dont expect the best. I don't see how 1 Plant same strain can be so much bigger than another of the same strain. I feel I should have left them in smaller homes first and moved them too soon but some seem to be just fine.

The biggest one in the picture is the biggest (White Russian)
The one that doesn't have support (White Russian)
The one in the wheelchair (Afghan Kush)

 
Your medium looks very dry, when you water make sure you water enough so all the soil becomes wet. And you should not be digging down to see how the roots are doing, disturbing the roots will stress the plant and cause it to halt growth until it recovers.