What position/role/duty training for young players on the senior team?

[SmoothKiminal]

Hi all. So basically I've signed two 16-year-olds and stuck them in my senior team as my U-19s isn't good enough to develop players yet and I don't have a Reserves team. One of them is a central defender and the other is a striker and I'm wondering what to train them as. I play with Ball Playing Defenders on defence and with a Deep Lying Forward on support. Should that be their individual focus or should I train them as a Libero and Complete Forward until they're older?

Added pictures for reference.

Thanks in advance.