You don't give much info about the trees, soil, watering etc. so I will have to be pretty general. The Serissa will survive indoors if it gets good light and care. The cherry needs to be out doors. Cherries are pretty cold tolerant. My suggestion would be to let it go dormant (loose all its leaves) and put in your garage or some protected place where it will stay between 25 and 40 F. Water it every week engough to keep it damp but not wet. Don't worry about lack of light during dormancy. Check your pots to see if they have gravel glued down on the surface. If they do remove it. Try to find a bonsai club in your area. Google "bonsai clubs" or some such thing and see what turns up. You can learn a lot in a club and keep from making dumb mistakes. Good luck, Jack