I'd recommend you fill them all up with soil, to the edge of the pot. It'll make them sprout roots from the stem that goes under, and support the rest of the plant. Not sure why they're so small at week 5, they look a little sickly and the one you snapped might not recover for a long time. Not sure what's making them grow so slow tho.
- Once you've filled the pots, get a fan going.. Careful not getting it too close at first tho, they're very skinny so it might damage them.. And then set it closer, as the stem gains some thiccness.
I hope you start seeing some growth soon.