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They are likely underwatered. I would recommend increasing water. This article will help with how often to water containers:
https://www.gardeningknowhow.com/special/containers/container-plant-watering.htm

If the geranium flower began to form pods these can be collected.

Gather the pods before they burst open.
Dry the pods completely and store in a sealed dark container in a cool area.
Sow the seeds in February for a the same years as they are slow growing. 13 to 15 weeks to flower after sprouting.

Remember if the plant is a hybrid the seeds may be sterile and would most likely not be true to the parent plant.

Cuttings are the recommended method of propagation for Geraniums.

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

Sounds like an amazing specimen.
Here are a couple of links that will help you get your plant pruned.

https://www.gardeningknowhow.com/ornamental/flowers/geranium/pruning-geraniums.htm
https://www.gardeningknowhow.com/ornamental/flowers/geranium/geranium-care.htm

sounds like your spoiling your geraniums too much water, I never feed mine and they are very happy

Did you fertilize? Oftentimes, this is a result of too much nitrogen in the soil and not enough phosphorus. Try adding some phosphorus rich fertilizer (Bloom booster) or bone meal to the soil around your plants.

Yes, you just pinch the spent flowers off. And, by pinching them off, you encourage the plant to bloom more. This article will explain about it: https://www.gardeningknowhow.com/ornamental/flowers/fgen/deadheading-flowers.htm