if I forged several checks for small quantities what can I do not to end up in jail and pay that person back?

You did not say if the cases have been filed yet. If not, there will be no arrest if you immediately pay the checks and there is no loss because, without a filing there is no criminal prosecution. If the bank notifies the police or your brother does you need legal representation. Each county has different rules as to how these cases are handled. The offense is completed when the forgery happened so if it is filed it can be prosecuted even if you have made restitution .