Calculating the equilibrium constants for parallel reactions
You can combine the two chemical reactions into a single global reaction scheme by adding them:
\begin{align}
\ce{A + B&amp;&lt;=&gt;C + D}\tag{1}\\
\ce{A + B&amp;&lt;=&gt;C + E}\tag{2} \\ \hline
\ce{2A + 2B &amp;&lt;=&gt; 2C + D + E}   \tag{Global}
\end{align}
and the equilibrium constant for this overall reaction scheme is equal to the products of the two equilibrium constants:
\begin{align}
K_\mathrm{eq,global} &amp;= K_\mathrm{eq,1} K_\mathrm{eq,2} \\
&amp;= \frac{\ce{[C]^2[D][E]} } {\ce{[A]^2[B]^2}}
\end{align}
(where $\ce{[i]}$ denotes either molar concentration or partial pressure of component i). You do not need to adjust the final total pressure or mole amounts.