Try to use l3keys.

packages/Graphics.sty

@@ -7,10 +7,10 @@
 
 \RequirePackage{wrapfig2}
 
-\providelength{\iconsize}[0.25in]
+\ProvideLength{\iconsize}[0.25in]
 
-\providelength{\@InlineGraphicHeight}[12pt]
-\providelength{\@InlineGraphicOffset}[-2pt]
+\ProvideLength{\@InlineGraphicHeight}[12pt]
+\ProvideLength{\@InlineGraphicOffset}[-2pt]
 
 \NewDocumentCommand{\InlineGraphic}{
 	O{\@InlineGraphicHeight}
@@ -89,34 +89,95 @@
 
 \RequirePackage{tabularray}
 
-\providelength{\twinfigspace}[3pt]
-\providelength{\twinfigwidth}[
-	\textwidth / 2 + \bigfloatoverhang - \twinfigspace
+\ProvideLength{\twinfigspace}[3pt]
+\ProvideLength{\twinfigwidth}[
+	\textwidth / 2 + \bigfloatoverhang * 3 / 2 - \twinfigspace
 ]
 
+\ExplSyntaxOn
+
+\dim_new:N \l_twinfig_overhang
+\dim_new:N \l_twinfig_width
+\dim_new:N \l_twinfig_space
+\fp_new:N \l_twinfig_offset
+\str_new:N \l_twinfig_placement
+\str_new:N \l_twinfig_valign
+
+\keys_define:nn{twinfig}{
+	overhang	.dim_set:N	= \l_twinfig_overhang,
+	overhang	.initial:e	= \bigfloatoverhang,
+}
+\keys_define:nn{twinfig}{
+	placement	.str_set:N	= \l_twinfig_placement,
+	placement	.initial:n	= {htpb},%\bigfloatplacement,
+}
+\keys_define:nn{twinfig}{
+	offset		.fp_set:N	= \l_twinfig_offset,
+	offset		.initial:n	= {2.0},%\bigfloatoffsetratio,
+}
+\keys_define:nn{twinfig}{
+	valign		.str_set:N	= \l_twinfig_valign,
+	valign		.initial:n	= {m},
+}
+\keys_define:nn{twinfig}{
+	width		.dim_set:N	= \l_twinfig_width,
+	width		.initial:n	= {3.14in},%\twinfigwidth,
+}
+\keys_define:nn{twinfig}{
+	space		.dim_set:N	= \l_twinfig_space,
+	space		.initial:n	= {3pt},%\twinfigspace,
+}
+	\keys_log:nn{twinfig}{overhang}
+	\keys_log:nn{twinfig}{placement}
+	\keys_log:nn{twinfig}{offset}
+	\keys_log:nn{twinfig}{valign}
+	\keys_log:nn{twinfig}{width}
+	\keys_log:nn{twinfig}{space}
+
+\typeout{\the\l_twinfig_overhang}
+\typeout{\l_twinfig_placement}
+\typeout{\fp_use:N \l_twinfig_offset}
+\typeout{\l_twinfig_valign}
+\typeout{\the\l_twinfig_width}
+\typeout{\the\l_twinfig_space}
+
+\ProcessKeyOptions[twinfig]
+
 \NewDocumentCommand{\twinfig}{%
-	% Big Float overhang.
-	O{\bigfloatoverhang}
-	% Float placement.
-	O{htpb}
-	% BigFloat offset ratio.
-	O{\bigfloatoffsetratio}
-	% First graphic file.
+	% #1: Big Float overhang.
+	%O{\bigfloatoverhang}
+	% #2: Float placement.
+	%O{htpb}
+	% #3: BigFloat offset ratio.
+	%O{\bigfloatoffsetratio}
+	% #1: Key=value options.
+	O{}
+	% #2: First graphic file.
 	m 
-	% First label.
+	% #3: First label.
 	>{\TrimSpaces}m 
-	% First caption.
+	% #4: First caption.
 	>{\TrimSpaces}m 
-	% Second graphic file.
+	% #5: Second graphic file.
 	m 
-	% Second label.
+	% #6: Second label.
 	>{\TrimSpaces}m 
-	% Second caption.
+	% #7: Second caption.
 	>{\TrimSpaces}m
+	% #8: Image vertical alignment.
+	%O{m}
 }{%
-	\begin{BigFloat}[figure][#1][#2][#3]%
+	\keys_set:nn{twinfig}{#1}%
+
+\typeout{\the\l_twinfig_overhang}
+\typeout{\l_twinfig_placement}
+\typeout{\fp_use:N \l_twinfig_offset}
+\typeout{\l_twinfig_valign}
+\typeout{\the\l_twinfig_width}
+\typeout{\the\l_twinfig_space}
+	\begin{BigFloat}[figure][\l_twinfig_overhang][\l_twinfig_placement][\l_twinfig_offset]%
 		\begin{tblr}{%
-			colspec	= {*{2}{Q[c,m,wd=\twinfigwidth]}},%
+			colspec	= {*{2}{Q[c,\l_twinfig_valign,wd=\l_twinfig_width]}},%
 			hlines	= {0pt},
 			%vlines,% For debugging. Comment out when done.
 			hborder{1,Z} = {%
@@ -128,26 +189,26 @@
 				rightspace	= 0pt,%
 			},%
 			vborder{2} = {%
-				leftspace	= \twinfigspace,%
-				rightspace	= \twinfigspace,%
+				leftspace	= \l_twinfig_space,%
+				rightspace	= \l_twinfig_space,%
 			},%
 		}%
 			\vfill
 			\captionsetup{type=figure}%
 			\includegraphics[%
-				keepaspectratio,width=\twinfigwidth%
-			]{#4}%
-			\captionof{figure}{#6}%
-			\label{fig:#5}
+				keepaspectratio,width=\l_twinfig_width%
+			]{#2}%
+			\captionof{figure}{#4}%
+			\label{fig:#3}
 			\vfill%
 			&%
 				\vfill
 				\captionsetup{type=figure}%
 				\includegraphics[%
-					keepaspectratio,width=\twinfigwidth%
-				]{#7}%
-				\captionof{figure}{#9}%
-				\label{fig:#8}
+					keepaspectratio,width=\l_twinfig_width%
+				]{#5}%
+				\captionof{figure}{#7}%
+				\label{fig:#6}
 				\vfill%
 			\\%
 		\end{tblr}%