Now don't get TOO excited Mel, but I think I know what your plant problem is! You say the sun shines in the house from all directions? Well, the worst thing you can do is water a plant in full sunlight! Its guaranteed to kill it! In the summer I keep my plants alive longer (outside and in,) by watering as the sun goes down. If you water onto sun-baked earth, it gives the plant a shock to the system and they will die!
So, try watering in the evenings, putting water into the drip tray, and I think you'll see the difference!! Good luck!
