I think that with the chicks in with them they would have had enough body heat to stay warm if they were all huddled together, they are 3 wks and have some feathers. If it's just the 5 keets by themselves they may have gotten chilled. How are they acting? If they are all huddled in a pile acting lethargic and peeping loud then they got chilled, just warm them up they should be ok. At 3 wks old you may want to switch out the bulb in the lamp to just a regular 60 watt bulb for their heat source, and if the days are really warm only use it at night (just be sure to remember to turn it back on, lol).
And yes, it's fine to keep them all together... keets/Guineas are happier in larger numbers (so even the chicks are a comfort to the keets). The keets need to be on high protein starter feed tho, not a lower protein chick starter. Some raise mixed flocks on 24% protein starter feed and they do ok, but my keets do much better on 27-28% protein game bird/turkey starter.
Your darker keets are Pearl Greys (they have a wide center head stripe) not Royal Purples... and I can't see the head stripes on the 2 lighter keets, but in that pic they kind of look thin and broken, without a big wide center stripe... which would make them Coral Blues. If they have the same type of head markings as the Pearl Greys do then they are Lavenders.