It doesn't take much to damage a small watermelon. Check it in a week or so and if it still looks alright it's probably OK. My experience is with hail damage. Any dent or mark in the outer rind usually causes the fruit to rot as it nears maturity.

Not sure what to say about the stepped-on melon, you'll just have to watch it and see if there is any damage that causes it to rot. As for the melons growing close to each other, they will be fine. Here's a pic from my melon patch last year around this time, both of these grew bigger (I think they ended up touching each other) and ripened and were deliciious!
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As long as you didn't crack the rind you should be ok. I had some insects dig at my watermelons when they were small. The insects (or chipmunk, not sure) took some pretty good digs out the rind, but luckily it wasn't too deep. They scared over and grew ok.