I brought 2 of my 4 hibiscus plants in for the winter?

That is normal, it is the shock of being in a different climate than they were outside. You should soon see new leaves coming out where the old ones yellowed and fell off. I have 6 large pots and two window boxes (with 3 small ones in each) of hibiscus that I bring in for the winter, so far all six large pots have some yellowing and dropping off, with the window boxes not doing it so far. This article may help you understand better what is going on with your plants. There are also many articles on hibiscus that may interest you that are at this site.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-leaf-drop.htm

I hope this helps ease your worries, Rosemary!

I'll definitely read it. Thank you so much.

Keep them cool (55-65) and water when they are dry. Ideally if you want to bring your hibiscus indoors to over winter them, they should be grown in pots outside all season, not planted directly in the ground. Too much water or not enough can result in hibiscus leaves turning yellow. ... Failing to give hibiscus plants enough water can also cause the hibiscus leaf to yellow. Check the soil with your finger to ensure the plant is getting enough water. Self-watering pots are also a good way to alleviate these problems. Location causing hibiscus yellow leaves After allowing the plant to enter dormancy, bring it indoors and keep it in a cool, dark place for a couple months, then cut the hibiscus back and place it in a sunny window. Resume regular watering. When the hibiscus shows new growth, give it a boost of fertilizer. Once spring returns, the plant can be moved outdoors. If your hibiscus has yellow leaves, has stopped blooming, or looks wilted after moving it, the plant may be suffering from stress. This is a common occurrence and can be expected when moved to a different environment. Pests causing hibiscus yellow leaves In addition to yellowing, the hibiscus leaf may become mottled with markings on the underside. This can be the result of pests such as spider mites. If left untreated, the stressed plant will eventually lose all of its foliage. If you suspect these pests, spray the plant with soapy water or an appropriate form of pesticide. However, take care not to overuse pesticide, as this may also contribute to hibiscus yellow leaves.

Read more at Gardening Know How: Answers To What Causes Hibiscus Leaves Turning Yellow https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm

I have been doing this for 10 years. My hibiscus have lasted that long. I keep them potted all year. They will turn yellow in the fall. Keep them in the house if you choose and keep slightly moist not wet . When the flowers are gone trim the bush back a bit, New leaves grow in pretty quickly and they do fine. Oh. Use plant food once a month one that will promote healthy leaf growth like 30-30.

Put them back out in May. They need a lot of light indoors as well.