Your legal base as an adult relative is:
- Kapitel 2 - Einreise und Aufenthalt im Bundesgebiet (§§ 3 - 42)
- Abschnitt 6 - Aufenthalt aus familiären Gründen (§§ 27 - 36)
- § 36 Nachzug der Eltern und sonstiger Familienangehöriger
Commonly called "Family reunification".
The law basically says that family reunification for minors and spouses is allowed (§29), others only in specific cases of hardship (§36).
Those cases of hardship are decided case-by-case. Normally, courts will rule that the binding between parents and non-minor children are not of such a kind that separation constitutes a case of hardship. "außergewöhnliche Härte" (case of hardship) applies for example if the child cannot live a life of their own, maybe because of a (mental) disability, chronic illness or trauma.
Whether you can find a lawyer that is so good (or sleazy) that he can bend the law to your will, I cannot say. Maybe you can find some other option to stay in Germany that does not rely on your relatives already being here. Maybe you qualify for a blue card on your own?