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This article will help you:
https://www.gardeningknowhow.com/composting/ingredients/coffee-grounds-gardening.htm

This article will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-and-calcium.htm

One option is to use compost, perhaps liquid tea form. It will not harm pets if they should try to ingest it, which they shouldn't. These articles may help: https://www.gardeningknowhow.com/composting/basics/compost-tea.htm
https://www.gardeningknowhow.com/composting/manures/manure-tea.htm

Likely not. This is stunted growth caused by a lack of oxygen to the roots. There is not much you can do for them other than to try to improve their drainage.

This article will explain more about what epsom salt does:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/epsom-salt-gardening.htm

Yes, you can. Make sure that you water the plants well before you fertilize to keep the fertilizer from burning the roots.

Get a soil test before you add anything more to your garden. Your local extension office offers soil tests kits with directions on how to use them. Your soil sample goes to your state lab for analysis and they will be able to tell you exactly what amendments you may need to add as well as how much of each. The fee for the service is nominal. It's a cheap and easy way to make sure your ground is at it's optimum for next spring's garden.