The greenhouse has a mortar base, which is isolated and is deep into the soil, the soil in the greenhouse is isolated from the outside soil. I am thinking if making hols in the soil for the pots, burry the whole pot into the soil to regulate its temp, and just open the greenhouse while sunny , to not get so hot inside.
I have not watered them for around a month, the soil in their pots is moist, I will keep them on the dryer side.
What's the lowest temp they could handle, I know the rootstocks give some hardiness to, and that the lemons might be more cold sensitive. In the nursery I bought the grafted pomello and kumquat from, one of the employees said they keep them in the greenhouse without aditional warmth, and that the citruses were handling temps around minus 6-7 C.