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This can be done, best, when the shrub is dormant, or not growing. Just dig far enough around (a foot or so) to get the root crown. This can be relocated, and watered slightly until it has settled in. Allow it to finish its dormancy and it will regenerate in spring. This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/rose-of-sharon-bush.htm

A small piece of wood makes a good spacer. You could also tie each of those branches to other branches that would pull them apart. If you do choose this option, make sure to use rubber plant tie material to avoid harming the shrub.

Sometimes it is necessary to prune so that it can reshape its self after the pruning.

That is actually one of the more interesting specimens. There are very many varieties, and most will do just fine in your area. You are right on the very edge of what they can tolerate, but with a little shade, you can keep this thing looking good. As far as any vendors in that area... You will have to look around. I am unfamiliar with that area. There are many online nurseries that will ship to just about anywhere, though.

This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/rose-of-sharon-bush.htm

Rose of sharon is prone to fungal infection and bacterial leaf spot diseases. Without a picture, it isn't possible to guess what is bothering your shrubs. If you are in the USA, your county has an extension office where you can take a sample for diagnosis. Use this link to find your office: http://pickyourown.org/countyextensionagentoffices.htm

As soon as danger of frost has passed (which it has!) , your seedlings can be planted out.
Make sure you harden off the seedlings by slowly acclimating them to the outdoors.
https://www.gardeningknowhow.com/ornamental/shrubs/rose-of-sharon/rose-of-sharon-bush.htm
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/how-to-harden-off-your-seedlings.htm

Are the bushes receiving enough sunlight? The previous owner may have planted them in a full sun spot but growing trees now have them in shade. It tolerates part shade (4 hrs sun daily) but will flower more is it receives at least 6 hrs. Like other hibiscus, it is late to leaf out in spring. Since it is a rugged shrub, I would think that the broken one will send up new shoots. It often self-sows so look for seedlings. The soil should be damp, not wet and not super dry. Other than that, it is an easy to grow shrub. Have you looked for pests like aphids? Are there any signs of disease? Here is an article that describes leaf spot and fungal root rot. http://homeguides.sfgate.com/treat-diseases-rose-sharon-tree-36426.html