High penetration of solar photovoltaics (PVs) in distribution systems necessitates the need for embedding an efficient control strategy for reducing loss and confining nodal voltage within an acceptable range. In this study, a multi-timescale Volt/VArcontrol model is proposed to co-optimize the traditional capacitor banks with off-unity power factor inverters of PVs and electric vehicles (EVs). First, in an inter-hour scale, capacitor banks are scheduled. Next, in an intra-hour scale, the inverters and EVs provide power support to supplement the inter-hours decision. The coordination of resources between two different time scales is performed using a risk-constrained stochastic problem with uncertainty modelling. The prediction errors associated with PV generation are modeled by Gaussian Mixture model (GMM), capturing the drastic changes of solar generation due to the weather-related effects. Finally, the merits of the proposed model are shown on a modified IEEE 33 bus system.