Geraniums actually make decent houseplants, if you can provide them with lots of bright light. They like a cool temperature, so even if you keep your thermostat low, they should be happy. But they’ll start to look gangly and gawky if you don’t provide enough light. A bright west or south facing window or grow lights are crucial. Just don’t keep the plants too close to a window that gets a draft.
Bring your plants indoors before the first frost. I recommend bringing all plants indoors before you have to shut all the windows and turn on the heat. It gives them time to adjust before the drop in humidity that central heating brings.
Check your geraniums closely for signs of insects or disease. Dig and pot up healthy plants and prune them back by about 1/3. It may seem harsh, but it will help them adjust in the long run. Give them a good dose of water when you first bring them in, then allow the soil to dry out between waterings. Geraniums seem to like a little drought stress; it keeps them blooming more frequently.
Keep an eye out for the usual indoor pests like aphids, spider mites and fungus gnats. If your geranium is happy, it will continue to grow and bloom, although not as well as it does outdoors in summer. If it looks like it's struggling to stay alive, consider letting it go dormant until spring.