Your temperatures are ideal for N. 'Miranda'. We find potting the two plants up individually actually stimulates more growth, especially ground shoots. Gently remove some of the peat from the root ball and move into a bigger pot. Use a somewhat peaty mix, as this is what the plants are accustomed to growing in. I take our regular Nep mix and add 50 percent more peat. Another good recipe is to use the Home Depot Phalaenopsis Mix and mix it 50/50 with Lambert Canadian Sphagnum Peat.
A word of warning- N. Miranda is a large grower, with leaves over two feet long and pitchers up to a foot long.