This is really puzzling me. The larger one looks like a Japanese maple. (About seven years ago OH and I spent several happy hours sowing chitted seeds of a variety of maples, including Snakebark, Acer cappadocicum rubrum, and various Japanese maples. The supplier chitted them for us so when we got them in small polythene bags with compost, each had a little root. We didn't need to stratify them - just sowed them, and a good proportion came good. I have several in my garden now.
The seedlings looked like yours, but so do sycamore (sorry I keep coming back to them). Thing is, I can imagine your friend's father sowing maple seeds pretty densely in a seedbed, digging them up and potting them to take away, and some seeds may not have germinated right away. Sometimes they can take two or more years to break dormancy. BUT, it's four years on since you got the original one, and suddenly some more seeds have germinated. That's surprising ( to me anyway), but I guess it's possible.
The alternative is that some seeds from another tree have landed in the pot. My mother in law kept seedlings in pots outside until she had found them a home, but often by the time I got round to planting them there were birch, beech and cotoneaster seedlings among them. But you say there are no trees near you. So maybe they ARE the same as the bigger one.
Anyway, you will soon know, when the true leaves of your seedlings open fully.
As for the sickly seedlings, I agree with Alina. The roots may have been damaged, and yellowing could be because the compost is too wet for them. I would try to keep them out of the rain, but outside, to let the compost dry out a bit. Don't be disheartened if you lose a few. that's normal.
