Question about Gigaset C530 Ip

does anyone know if it is possible to operate 3 such devices in the same network (that would be 6 voip connections ... is that possible at the same time? the additional analogue channel is not an option) and then 2 pieces of C530 HX each, so that in the end with 9 devices one can safely make calls via 6 voip connections at the same time? (fibre-optic internet with fritzbox is available)