Its a personal decision..you have to decide what you think is best for your flock ...
Im curious why did you split them this time of year ?
I put my 2 flocks together ...for heat in the winter ( young ones & old ones )
I've got all mine running together too except for the ayam cemanis. My silkies, cochins, frizzles, naked necks and everybody else are together though. Heat lamps scare me not only because of the risk of fire, but because if they go out and the temperature drops quickly all the birds can die from the shock of it.