How to add a research paper (class) to a thesis (class) in one OverLeaf file

Question

I have a thesis class that has the following tex file as a main file and it is called: thesis.tex

    %------------------------ Preamble and bibliography resources
    \documentclass[12pt,oneside]{book}[usenames,dvipsnames,svgnames,table]
\usepackage{style/title}[PhD]
\input{frontmatter/preamble} 

\makenomenclature
\usepackage{multicol}
\usepackage{graphicx}
\usepackage{dirtytalk}
\usepackage{titlesec}
\usepackage{xpatch} % for \xpatchcmd
\usepackage{lipsum} % for \lipsum to produce dummy texts 
\usepackage{bibentry}
% Add your bibtex file here
\addbibresource{references.bib}
%------------------------ Main Document --------------------------
\begin{document}
\newcommand{\coo}{\ensuremath{\mathrm{CO_2}}}
\newcommand{\chh}{\ensuremath{\mathrm{CH_4}}}
\newcommand{\wv}{\ensuremath{\mathrm{H_2O}}}
\newcommand{\radiance}{\ensuremath$\mathrm{Wm^{-2} sr^{-1}\mathrm{\mu m^{-1}}}$}
\newcommand{\oo}{\ensuremath{\mathrm{O_2}}}
\newcommand{\nn}{\ensuremath{\mathrm{N_2}}}
\newcommand{\oz}{\ensuremath{\mathrm{O_3}}}
%-------------- Information For The Title Page
\title{thesis title}
\author{name}


%-------------- Front Matter
\frontmatter
\maketitle

\include{frontmatter/abstract}
\include{frontmatter/acknowledgments}
 \include{frontmatter/declaration}
\include{frontmatter/publications}

%-------------- Table of contents
\cleardoublepage
\phantomsection \pdfbookmark[0]{Contents}{Contents} 
\tableofcontents
\addcontentsline{toc}{chapter}{\listfigurename}
\listoffigures
\addcontentsline{toc}{chapter}{\listtablename}
\listoftables



%-------------- Chapters
\cleardoublepage
\mainmatter
\titleformat{\chapter}[display]{\sffamily\huge\bfseries}{\filleft\chaptername \ \thechapter}{4ex}{}[{\titlerule[1.5pt]}]
\include{Chapters/chapter1}
\include{Chapters/chapter2}
\include{Chapters/chapter3}
\include{Chapters/chapter4}
\include{Chapters/chapter5}
%-------------- Bibliography


\cleardoublepage
\phantomsection
\addcontentsline{toc}{chapter}{References}
\printbibliography
%-------------- Appendices
\cleardoublepage
\appendix
\include{appendices/Papers}
\include{appendices/Optica-template}
\cleardoublepage
\phantomsection
\addcontentsline{toc}{chapter}{Appendices}



\end{document}

This produces a pdf file of the thesis file that ends with the appendices.

I have a research paper that has a different class and style. The main tex file for the journal paper is called: Optica-template.tex and looks like this:

\documentclass{optica-article}
\journal{opticajournal} % for journals or Optica Open
\articletype{Research Article}
\usepackage{lineno}
%%%%%%%%%%%%%%%%%Added packages %%%%%%%%%%%%%%%%%
\usepackage{float}
\usepackage{tikz}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\linenumbers % Turn off line numbering for Optica Open preprint submissions.
\begin{document}
body
\bibliography{references1}
\end{document}

Now, my question is: How can i compile the these two classes to have a one pdf file where the paper is places at the end of the thesis in the appendices?

It throws errors like this one:

LaTeX Error: Can be used only in preamble.
You have used a command in the main body of your document which should be used in the preamble. Make sure that \documentclass[…]{…} and all \usepackage{…} commands are written before \begin{document}.
Learn more
See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...
l.1 \documentclass
                  {optica-article}
Your command was ignored.
Type  I <command> <return>  to replace it with another command,
or  <return>  to continue without it.
! Undefined control sequence.
l.3 \journal
            {opticajournal} % for journals or Optica Open
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., \hobx'), typeI' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

and does not recognize the references (i named the references tex files differently for the thesis and the paper).

I would appreciate your guidance.