Unless you are constrained to legacy fonts, it is much easier and more flexible to use the modern toolchain with fontspec package and system fonts, and compiling with xelatex or lualatex. You can define as many (or as few) font switches as you need. OpenType font features become available also.

(Fonts coloured to highlight the switching.)
MWE
\documentclass{article}
\usepackage{xcolor}
\usepackage{lipsum}
\usepackage{fontspec}
\newfontfamily{\fraleway}{Raleway}[Colour=blue]
\newfontfamily{\flato}{Lato}[Colour=red]
\newcommand\parnum{5}
\begin{document}
\sffamily
This is default sans.
\lipsum[\parnum]
\fraleway
This is Raleway.
\lipsum[\parnum]
\flato
This is Lato.
\lipsum[\parnum]
\normalfont\sffamily
This is back to default font.
\lipsum[\parnum]
\end{document}
To set a font as the sans font for a document, the \setsansfont{...} command is used.
Here, Raleway is made the default sans:

MWE
\documentclass{article}
\usepackage{xcolor}
\usepackage{lipsum}
\usepackage{fontspec}
\setsansfont{Raleway}
\newfontfamily{\fraleway}{Raleway}[Colour=blue]
\newfontfamily{\flato}{Lato}[Colour=red]
\newcommand\parnum{5}
\begin{document}
\sffamily
This is default sans. (Raleway) %{\tiny\fontname\font\ }
\lipsum[\parnum]
\fraleway
This is Raleway. %{\tiny\fontname\font\ }
\lipsum[\parnum]
\flato
This is Lato. %{\tiny\fontname\font\ }
\lipsum[\parnum]
\normalfont\sffamily
This is back to default font. %{\tiny\fontname\font\ }
\lipsum[\parnum]
\end{document}