Rukmini devi wants to install Caitanya Mahaprabhu, so Caitanya Mahaprabhu can be installed on the right side of Krishna, as you have seen in pictures from our Gaudiya Math temples. Nityananda there is no need. Simply three compartments, Gauranga and Spiritual masters in the first compartment, Radha and Krishna in the central compartment, and Lord Jagannatha in the third compartment. But if there is no room for three, then Radha-Krishna with Lord Caitanya on the right side with them, pictures of Spiritual Masters below.
Letter to Rupanuga, 3 May, 1972