# GraphicsGrid and BarLegend combined

I have constructed this contour plots for a project

ContourPlot[
(2.1 - a^2 + 2.1 b) (-2 + (2.1 (1 + b))/a^2),
{a, -1.5, -0.5}, {b, -1, 1},
PlotRange -> All,
ContourShading -> {RGBColor[0.16, 0.5, 0.5], RGBColor[0.51, 0.35, 0.25]},
Contours -> {Automatic, 1},
PlotLegends ->
{BarLegend[Automatic, LegendMarkerSize -> 180,
LegendFunction -> "Frame", LegendMargins -> 5]},
PlotLabel -> "Contour Plot", LabelStyle -> {Thick, Black},
Mesh -> 1, MeshStyle -> Red, MeshFunctions -> {#1 &}
]

I have also the following contours

g2=(2.1 + (-1. - 6.6 a) a^2 + 2.1 (1 - 0.6 a^3) b) (-2. + (2.1 (1 + b))/   a^2 - 0.2 a (33 + 6.3 b))
g3=(2.1 + a^2 (-1. + 6.6 a) + 2.1 (1 + 0.6 a^3) b) (-2. + (2.1 (1 + b))/   a^2 + 0.2 a (33 + 6.3 b))
g4=(2.1 + a^2 (-1. + 14. a^2) + 2.1 (1 + 2. a^4) b) (-2. -    2. a^2 (-7 - 2.1 b) + (2.1 (1 + b))/a^2)

and I want to combine the four contours with GraphicsGrid and have a common BarLegend in the bottom of the figure (similar to the bar legend of the first contour plot). However I was unable to do that. Any suggestions?

This is kinda intro. You can improve this. You should define different range for each plot.

g = {(2.1 - a^2 +
2.1 b) (-2 + (2.1 (1 + b))/a^2), (2.1 + (-1. - 6.6 a) a^2 +
2.1 (1 - 0.6 a^3) b) (-2. + (2.1 (1 + b))/a^2 -
0.2 a (33 + 6.3 b)), (2.1 + a^2 (-1. + 6.6 a) +
2.1 (1 + 0.6 a^3) b) (-2. + (2.1 (1 + b))/a^2 +
0.2 a (33 + 6.3 b)), (2.1 + a^2 (-1. + 14. a^2) +
2.1 (1 + 2. a^4) b) (-2. -
2. a^2 (-7 - 2.1 b) + (2.1 (1 + b))/a^2)};

Legended[Multicolumn[
Table[ContourPlot[g[[i]], {a, -1.5, -0.5}, {b, -1, 1},
PlotRange -> All,