Pic 1. The silhouette doesn't look right, it is too black, have you burned in the area to completely get rid of even the slightest detail? You are not shooting directly into the sun so that effect to much. The couple are too close which is just making them look like a giant 2 headed monster. Space silhouettes apart give each person a clear outline.
Pic 2. It's OK, personally I am not keen on chopping people up to that degree. Pulling back little would of gotten both the male and female. Very central composition. A square crop (1:1 ratio) might make the picture settle, or while it doesn't have to be rule of thirds, just being off centre slightly allows the eye to wander across the frame.
Pic 3. It's a nice moment, but the first thing that I notice is her hand in his crotch, he looks like he is guiding her hand to his special place... her arm is awkwardly twisted in the process.
This couple are heavy set, in casual clothes, so having them sit down makes them look enormous! Either compose them so you are just seeing their faces, or avoid sitting them down all together.
Pic 4. Same as pic 1. they are squishing into each other, which is adding weight, both wearing similar colours. If they had contrasting colour tops it would provide that separation.
Pic 5. I think I am seeing what you are going for, but they are too close to you, and your DOF is far too shallow. The bridge is providing leading lines. So if they were 10 or more meters away from you, and you were at F8.... That would enable your central composition to work.
Pic 5. Again sat down makes them look larger. Had you stood above them and shot down, it would of gotten rid of double chins, and the perspective would have put their bodies further away from you, making them appear slimmer.
Pic 6. Leading lines are nice, squished posing is adding weight, I really think different coloured tops would of lessened that issue.
Pic 7. I didn't know railings could be so enthralling... It looks like they had a cool city scape in front of them. I would of stood them by the railings, stood myself on the bench. Shot the city scape at f8 over the shoulders of the couple, so you are "seeing" their perspective, but they are still in the photo.
The couple will probably love the photo's, I imagine the only photos they have are smart phone ones, so some good quality ones are always appreciated.
In future I would tell couples to wear contrasting colours, there is a reason why traditionally weddings have white dresses and darker suits.
It is much harder to pose heavier couples. Consider using focal lengths beyond 85mm as they are more flattering.
Keep practising, good luck!