Well, you've got two plants in that one container that isn't even filled with potting mix. A single zucchini plant will completely fill out that container. Your plants aren't even close to being full size yet and my guess is that they are already rootbound.

Also, you are trying way too many things at once. Adding fertilizer and then trying to flush it out with water completely negates the use of fertilizer to begin with. Allowing only few days in between for the fertilizer to get absorbed and used by the plants wasn't enough time to judge if it worked or not. Fish emulsion is a weak fertilizer to begin with and is not a quick fix. And Jobe's (depending on which specific product you used) may be ineffective in your situation. It does look like they probably need some fertilizer and while a well balanced liquid fertilizer will work quicker than a dry fertilizer it still takes time. Organic fertilizers take even longer to work than synthetic fertilizers.

My guess is that at this point you will probably need to water every day as well, even if the containers weren't overcrowded. But to be sure you need to stick your finger in the soil and feel the soil moisture. Every time you water you will be flushing nutrients out of the containers so you will need to fertilize frequently throughout the growing season. Fertilizing weakly weekly is a common adage of container growing.

Adding Tums isn't going to do anything. The calcium in it is not a form usable by plants. The neem oil could have burned your plants leaves if the temps were high or the oil wasn't diluted properly. The flowers are aborting because the plants are under stress.

Rodney