Very nice touch with the video. Fun to watch.
It would help us all to know what growing zone you are in...or otherwise location.
Oneeye covered the soil amendments very well. I'd just add that compost is your new friend. There are often free sources of material...leaves, grass clippings, etc. around the neighborhood to take advantage of...but whatever, get a compost pile going now...imediately.
On the three squash question...you have a couple of options. 1) Plant it as is. I like to plant my squash in small hills. Just hill up some amended soil and plant it as is. It grows better this way and harvests better and is less prone to problems with insects. 2) You could try to split the three into 2 or maybe 3 individual plants and plant those. It looks like you will likely loose the one on its side and the other 2 will make it. Its a bit tricky to split these and other plants but you need to learn a technique that works for you. Always do it wet, always take utmost care to not damage any roots, and kind of let the split happen where it wants to gently without forcing. For me, I would just plant the whole thing in a hill and watch them grow. Squash does fine planted as a threesome in a small hill.
An important, I should say critical, aspect of gardening is knowing when to plant which plant. For example, you mentioned water melon and lettuces in the same video. One is a hot weather plant (watermelon) and the other (lettuce) is a cool weather plant. Never growing in the same season depending on your location.
The other thing I would add is learn to plant what you like to eat. It is motivational.
Come back and see us often, especially after you have amended your soil and be sure to give us your growing zone.