Yes, I agree they are getting less light. You may be giving them too much water if you have gnats flying around. Plants in the house will dry out slower, and don't leave the pot sitting in a saucer full of water. Hibiscus do better in well drained soil and will rot in wet soil. It probably needs more direct light than your window provides especially if it is still trying to flower.
Happy gardening in Hawaii. Gardens are where people grow.