u21 and players

i recently built u21 facilities and at the end of my season i'll get 2 new players, will they be of good quality and do i have to pay to sign or they automatically get added to my team?

about players I wanted to ask that how can i get them to play better?
except for my strikers, my team doesn't go to a 8 or 9 rating very often and sometimes I see my best players at 6 or 5.
I use boosters to keep their morale high, I watch live matches, I even give a win bonus and condition full but i dont know why so low ratings :@ and some of them stopped playing good this season, last season they were beasts, and similarly my 3 star players have better ratings than the good players i have, is there anything i can do to make them play better?

Nope, at the end of your season the youth players will loose very soon a star....
They will not sign up auto. You have to sign them up manually, and for the best of the two players you will have to pay between 12-18 tokens.
The other player (3*) will be free

The stars depend on the quality of your youth facility. Last season I had the building at L3 and got a 3* (12 tokens AFAIRC) and a 1* (free).

I got both mid-season. Im signed the free 1*, checked his growth and was massively pissed. It would not have been possible to improve him to 3* and sell him until the end of the season, so I dumbed him. I tried to approximate the market value of the 3* and got a far better ratio than a money transfer (even one level higher). So I signed him and let him train with the team to become 4* and then sold him. So signing the better one for tokens made sense in my case (to me) at the start of the game (im Lvl 3) since money is a bottleneck. Keeping the bad one in the squad until the 1st day of the new season would have made sense when thinking of the new cup format, too. But I did not know it at that time.

You wrote you get both at the end of the season. That is BS. As Poker-32 already wrote the players get quickly one year older and decrease in value. I would suggest to dumb the better one that costs tokens and sign the other one for free, watch how pathetic he improves and dumb it after the cup draw has been made (1st day of new season)