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Blueberry plants are shrubs and can't be divided the way most perennials are; however, you could propagate them via their shoots, which are found around the base of the bushes. They can also be propagated through cuttings, both hardwood and softwood cuttings. Most propagation is done with hardwood cuttings, as they are easier to handle and are less perishable than softwood cuttings. However, softwood cuttings generally grow quicker. Here is more information on how to propagate cuttings: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm

As for pruning, this article should be of some help to you: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm

This article will help with fertilizing blueberries: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-fertilizer.htm

I would recommend using a slow release fertilizer, like Osmocote, on your muscadine vine during the spring/summer to make sure it gets enough nutrients.

How is your soil? It could be due to the pH of your soil. Blueberries like low soil pH; otherwise, the roots become blocked and the plant cannot take in any moisture or nutrients and will quietly wither and die. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm
https://www.gardeningknowhow.com/edible/fruits/blueberries/lower-soil-ph-blueberries.htm

No they are not compatible. This article will help with plants that are: https://www.gardeningknowhow.com/edible/nut-trees/black-walnut/black-walnut-compatible-plants.htm

This may signal a pollination issue. Without proper pollination, plants will normally abort their fruit/blossoms.

This may signal a pollination issue. Without proper pollination, plants will normally abort their fruit/blossoms.