Upload & Sell: On
Actually the first one looks good as it is, just snip a bit off the bottom to lose that bottom patch of grass. Your combined shot looks great. In terms of what's acceptable, pretty much we in here have followed the "as long as you declare the combining of shots" it's fine. Where people draw ethical lines is when it's not declared and it is passed off by the poster as a totally real moment in time.
You did good on it, and I think if you printed it, and hung it up, thst one photo would bring back 2 great memories for you.