if somethings wrong with the transmission, can very little weight affect it ? Like would added weight make it mess up if the transmission is bad ?
If something is wrong with the transmission, you have 2 viable solutions. Adjust or tighten the bands with an oil and filter change. If that doesn't fix it, get another used trans (unless you can find a cheap new one). The weight of passenger/s has no effect. Excessive tongue weight from towing a trailer might cause long term problems.
Yes, of course! It depends on how much weight you have added to it. Say your pulling a small trailer, even if it is empty, it will shift a lot harder or it will miss a gear or slip. I don't recommended you add too much weight to your car. You need to have it looked at, because if you keep driving it and it suddenly goes out, you are stranded there.
It's the same with any work; If one doesn't do their job the whole organization suffers. If the transmission is bad, weight may or may not affect it's misbehavior. The car weighs 5000 pounds, so your 40 pound nephew is not going to have much effect. If you don't want to be driving people around you can tell them it's your transmission if you want, or you can tell them the truth- they should stop bumming rides.