Bib(la)tex: multiple citations in one "References" entry + ordering issues

Question

I'm using the biblatex package for my thesis (class style: book -- although technically I'm using the MastersDoctoralThesis template from Gunn and Patel*).

*source: https://www.latextemplates.com/template/masters-doctoral-thesis

Let's say I'm starting to write the thesis from Chapter 2. I cite Ref3 and Ref4 from topic2.bib using \cite{Ref3} and \cite{Ref4}; they appear in-text and in the "References" section as [1] and [2]. No problem here, since these are the first citations I've made. However, what if I wanted to combine Ref3 and Ref4 into one "Reference" entry (so [1] in-text will appear as "[1] Ref3, Ref4" in "References"). In my experience, I would use \cite{Ref3,*Ref4}. However, I have found that this is not working here. I've tried using mcite, but it seems that Ref4 is simply being... absorbed?

Am I supposed to define a "MySet" command first, and then use \mcite{MySet,*Ref3,*Ref4}?

Let's say I now move to Chapter 1. I have just added Ref1 and Ref2 from topic1.bib to Chapter 1. These appear in my "References" as [3] Ref1 and [4] Ref2, even though they appear in the text before Ref3 and Ref4 of Chapter 2. In other words, my ordering in-text is [3], [4], [1], [2]. How can I fix this?

Here is the minimal working example:

\documentclass[12pt,english,singlespacing]{MastersDoctoralThesis}
\usepackage[
    backend=bibtex, 
    natbib=true,
    mcite=true,
    style=phys,
    citestyle=numeric,
    biblabel=brackets,
    giveninits=true,
    abbreviate=false,
    doi=false, url=false, isbn=false, eprint=true,
    sortcites=true,
    block=space,
    backref=true, backrefstyle=two,
    ]{biblatex}
\addbibresource{topic1.bib}
\addbibresource{topic2.bib}
\addbibresource{topic3.bib}
\usepackage[autostyle=true]{csquotes}
...
\begin{document}
\chapter{Chapter One}
When Mr Bilbo Baggins of Bag End announced that he would shortly be celebrating his eleventifirst birthday with a party of special magnificence, there was much talk and excitement in Hobbiton \mcite{Ref1,*Ref2}.
...
\chapter{Chapter Two}
In the land of Mordor \cite{Ref3} where the shadows lie \cite{Ref4}.
...
\printbibliography[heading=bibintoc,title={References}]
\end{document}

After LaTex + BibTex + 2x LaTex, my bibliography reads as

References

[1] Ref3

[2] Ref4

[3] Ref1

My sincere apologies for asking so many questions in a single post. Any guidance, as always, is highly appreciated!

Answer 1

There are two issues here

1. The mcite compatibility interface of biblatex has a slightly different syntax than mcite. Details can be found in §3.9.10 mcite-like Citation Commands of the biblatex documentation.

   In particular \mcite{Ref1,*Ref2} will not just add Ref2 to the bibliography entry of Ref1. Instead you will need to say something like \mcite{myset,*Ref1,*Ref2} to create a 'virtual' set entry myset containing both Ref1 and Ref2.

   Keep in mind that backend=bibtex, may not fully support mcite and dynamic sets. BibTeX support for a subset of the available features was added in v3.15 (2020-08-16), see https://github.com/plk/biblatex/issues/921 and https://github.com/plk/biblatex/issues/985.

2. Because you are loading style=phys, citestyle=numeric, you get the sort order sorting=nty, so all of your entries are sorted by author, title and year and not by occurrence in the text. I see little point in separating style and citestyle here, so I suggest you use

   style=phys,
   

   which automatically sets sorting=none,.

   Alternatively, if you insist on loading different styles, force sorting=none, explicitly and do yourself the favour of specifying bibstyle=phys, instead of style=phys, so you can see what is going on.

   bibstyle=phys,
   citestyle=numeric,
   sorting=none,
   

With those two issues fixed and using a .bib file that is available on every system with biblatex, I'd go with

\documentclass[12pt,english,singlespacing]{book}
\usepackage[
  backend=bibtex, 
  natbib=true,
  mcite=true,
  style=phys,
  biblabel=brackets,
  giveninits=true,
  abbreviate=false,
  doi=false, url=false, isbn=false, eprint=true,
  block=space,
  backref=true, backrefstyle=two,
]{biblatex}
\addbibresource{biblatex-examples.bib}
\usepackage[autostyle=true]{csquotes}
\begin{document}
\chapter{Chapter One}
Lorem \mcite{myset,sigfridsson,worman}.
\chapter{Chapter Two}
ipsum \cite{nussbaum}
dolor \cite{geer}.
\printbibliography[heading=bibintoc,title={References}]
\end{document}