Three column layout with three column footnotes

Question

I was able to find how to do three column layout of main text, for example using.

\documentclass[12pt]{book}
\usepackage[paperwidth=12.9in, paperheight=9.9in]{geometry}
\usepackage{multicol}
\usepackage{blindtext}
\begin{document}
\begin{multicols}{3}
\blindtext
\footnote{\blindtext}
\blindtext
\footnote{\blindtext}
\end{multicols}
\end{document}

Following the advice in Is a three-column footnote layout possible? I can also make 3 column footnotes.

\documentclass[12pt]{book}
\usepackage[paperwidth=12.9in, paperheight=9.9in]{geometry}
\usepackage{blindtext}
\usepackage{ledmac}
\footthreecolX{A}
\let\footnote\footnoteA
\begin{document}
\blindtext
\footnote{\blindtext}
\blindtext
\footnote{\blindtext}
\end{document}

But combining those never worked for me. How should I do it? In this example, it seems to try to fit the footnotes into the first third of each coumn. Result=crap.

\documentclass[12pt]{book}
\usepackage[paperwidth=12.9in, paperheight=9.9in]{geometry}
\usepackage{blindtext}
\usepackage{ledmac}
\usepackage{multicol}
\footthreecolX{A}
\let\footnote\footnoteA
\begin{document}
\begin{multicols}{3}
\blindtext
\footnote{\blindtext}
\blindtext
\footnote{\blindtext}
\end{multicols}
\end{document}

In the end, I'd like to be able to typeset a text like this:

Answer 1

YOu can now use reledmac which lets you set the column width for footnotes in columns. In ledmac the width in the threecolumn footnotes is fixed to .3\hsize and your case leads to really small footnote columns.

With reledmac you can set it back to \linewidth:

\documentclass[12pt]{book}
\usepackage[paperwidth=12.9in, paperheight=9.9in]{geometry}
\usepackage{multicol}
\usepackage{blindtext}
\usepackage{reledmac}
\arrangementX[A]{threecol}
\hsizethreecolX[A]{\linewidth}
\let\footnote\footnoteA
\begin{document}
\begin{multicols}{3}
\blindtext
\footnote{\blindtext}
\blindtext
\footnote{\blindtext}
\end{multicols}
\end{document}

If the result fits your needs I can't say…