Oh yes they are very young and need heat till about 6 weeks old.. I'm guessing you have power to the outside coop for a heat source then?Well they are only 2 1/2 weeks old. I thought Silkies didn't fully feather out until they are 4 months old or so? Wouldn't they need heat until they are fully feathered? It gets down to the upper 40s to lower 50s most nights.
Usually you have heat source temp around 35 degrees (Celcius) first week then reduce by 5 degrees a week... so around 6 weeks theyll be ok without heat. Mine were outside from week 5 without heat but temp was slightly warmer then yours.