If I understand your question correctly, the answer in my comment can help us. Changing \includegraphics with minipage environment in that answer, following code is extracted.
\documentclass{beamer}
\usetheme[numbering=none,block=fill]{metropolis}
%\setbeamerfont{frametitle}{size=\normalsize,series=\normalfont\bfseries}
\setbeamerfont{frametitle}{size=\Huge,series=\normalfont\bfseries}
\setbeamerfont{page number in head/foot}{size=\normalsize,series=\normalfont\bfseries}
\setbeamercolor{footline}{fg=black!2, bg=mDarkTeal}
\setbeamertemplate{frame footer}{My footline}
\makeatletter
\setlength{\metropolis@frametitle@padding}{0.7ex}% <- default 2.2 ex
\setbeamertemplate{footline}{%
\begin{beamercolorbox}[wd=\textwidth, sep=0.7ex]{footline}% <- default 3ex
\usebeamerfont{page number in head/foot}%
\usebeamertemplate*{frame footer}
\hfill%
\usebeamertemplate*{frame numbering}
\end{beamercolorbox}%
}
\setbeamertemplate{frametitle}{%
\nointerlineskip%
\begin{beamercolorbox}[%
wd=\paperwidth,%
sep=0pt,%
leftskip=\metropolis@frametitle@padding,%
rightskip=\metropolis@frametitle@padding,%
]{frametitle}%
\metropolis@frametitlestrut@start%
\insertframetitle%
\nolinebreak%
\metropolis@frametitlestrut@end%
\hfill
\begin{minipage}[t]{0.3\textwidth}
\small Prof.Dr. Nikola Tesla
\small Prof.Dr. John Doe
\end{minipage}
\end{beamercolorbox}%
}
\makeatother
\begin{document}
\begin{frame}{My frame title}
\begin{block}{Some itemize}
\begin{itemize}
\item \alert{Item 1}
\item Item 2
\end{itemize}
\end{block}
\begin{block}{Some maths}
\[\sum_{n=1}^{\infty}\frac{1}{n^2}=\frac{\pi^2}{6}=\zeta(2)\]
\end{block}
\end{frame}
\end{document}
