An interesting start, keep after it.
A few thoughts, strictly my opinion for you to chew on.
First, I find the perspective of looking up, a bit odd/unreal. Best way I can explain it is that I don't feel like I'm connecting with the subject. For the shot of the mature couple it's ok, for the rest it's a distraction. It emphasizes the things in the lower half of the frame so hands and knees become too large. Two suggestions/possibilities to remedy this; portrait orientation for the camera and include the feet in the shot or raise your camera to their eye level.
Second, is the framing. Two things here, most of the examples shown are 1- subject center and 2- wasted space left and right. Centered subjects can work (see Steve McCurry) but are hard to do well, for most shots getting the subject off center horizontally and vertically will help. Also again, shooting with the camera in portrait orientation may help, maybe a slightly longer lens or getting closer to the subject or doing some cropping for the print.