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Hibiscus do not winter well in most homes. Although it is a little late to prune, it will benefit from a pruning to help regenerate. They are also very heavy feeders, so repotting it in fresh soil, or adding some compost or other nutrients can help as well. Give it plenty of sun, but some afternoon shade until it recovers.

This article will help you to care for Hibiscus: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm

You can, either, cut it or leave it. Some fertilizer will help it to come out, though. They are very heavy feeders, so feed often in container.

Here is an article for more information:

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-container-care.htm

Some of that is common no matter what you do. This article should help:

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm

I believe these are both a Hibiscus! The tulipan has a different center.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm

Does your hibiscus get plenty of sunshine, water and fertilizer? Odd that your others thrive and this one doesn't. Has the soil ever been refreshed in the pot? You say you repotted to a larger size. Hibiscus like to be a little crowded so if you moved it to a much larger pot, that could be the problem. Also, inspect the leaves closely for signs of insects or disease.

Here is more information that may help.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm

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

Yes, you can repot them in the same pot. The fertilizer will probably help with blooming. Be sure to keep them well watered, especially since the weather turned hot.

Here is more information about growing hibiscus.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-container-care.htm