Keeping citrus indoors during the winter can be tricky if you don't have the right conditions. Give them plenty of sunshine (a south window is ideal), maintain even soil moisture, and keep the air as humid as possible. If you can keep the atmosphere around your plants humidified, they'll be under less environmental stress. Spider mites in particular thrive in dry conditions. If they appear, give the plant a forceful spray of water to wash them off. Insecticidal soap can also be helpful in controlling them. Scale and mealybugs are tougher to manage. Horticultural oil may help, though you may have to use rubbing alcohol swabbed directly on the pests. For severe infestations, a pesticide labeled for their control may be needed. Pruning can be done at any time to shape the plants, but in general they don't need much pruning indoors.