It appears you went offline without seeing my request for information. I don't want you to have to wait any longer, so I'm going to go ahead without your response.
I did some checking on the winter temperatures in Los Angeles. In a natural pond, the turtles would probably be able to survive by burrow into mud when it got too cool. without that option, the temperatures are not low enough for them to hibernate, but are likely to them to be lethargic and lose their appetites. That usually results in sickness.
The best option would be to bring them inside. Cupcake is a very large turtle and would require a 90 gallon tank. If you have a basement or a room where appearances don't matter, you could use a metal or plastic stock tank, rather than a glass aquarium. They are sold in farm/ranch supply stores and are much less expensive than aquariums. Set up the tank so there's a basking area where the turtles can climb out and dry off, and a water area. You want the water to be about 1 1/2 times as deep as the turtle is long. So Cupcake will need 15 inches of water.
The basking area should be kept at 88-92 degrees (29 to 32*C). The rest of the tank should be around 80*F to 85*F. You can adjust the temperature by raising or lowering the light fixture. You'll also need a submersible aquarium heater that will keep the water in the low 70*s. The basking light doesn't have to be something expensive from a pet store. If you live in an area that has farm stores, you can buy a metal light fixture made to keep baby chicks warm for just a few dollars. Don't buy the accompanying bulb, however. You need an ordinary incandescent bulb in the basking light. Hardware stores sell similar fixtures as work lights.
It's extremely important that you buy an additional light that produces UVB rays. A Reptisun 10.0 in the straight tube style (no compact fluorescents) is a good brand that does. If you choose another brand be absolutely certain it provides UVB rays. Don't take the word of pet store personnel, but read it for yourself. Full-spectrum, DayGlo, SunGlo, UV, or UVA are not the same thing. I'm putting a lot of emphasis on this because it's crucial to your turtle's health. Without this light, Metabolic Bone Disease (MBD) will develop because your turtle won't be able to produce vitamin D. Vitamin supplements are not a good replacement for the proper lighting. MBD causes a very slow and painful death.UVB bulbs must be replaced every six months as they lose their effectiveness after that, even though they may still look fine. Light that comes through a window isn't sufficient because the glass filters out most of the rays turtles need to stay healthy. To prevent MBD, turtles also need calcium. The easiest way to provide it is to place a cuttlebone in the tank. Cuttlebones are sold in bird departments of pet stores.
A good filtration system is essential because turtles are very sensitive to water quality. Water changes are also needed even with a filter.Turtles produce a huge amount of waste.
As for feeding, both turtles are old enough that they should be fed every other day. They need an omnivorous diet, even though they may prefer meat. Feeding too much protein, or feeding too often can result in kidney disease. Commercial food should make up 1/4 of the diet. Animal products (meat, earthworms, canned cat food) should make up another 1/4. The remaining half should be plant foods (dark lettuce like romaine, bits of strawberry or melon, etc.)
The following site has a care sheet for painted turtles. You can use it as a checklist to be sure all conditions and diet are right. http://www.austinsturtlepage.com/Care/caresheet-western_painted.htm
If after reading all this, you'd prefer to find a wildlife rehabilitator, just let me know by clicking on REPLY. Do the same if you have more questions. I hope you'll enjoy your tow house pets for the winter.
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