s[x_,y_,M_]:=-((y-(Sqrt[3])x-1)/2)M.M
u[x_,y_,M_]:=-((y+(Sqrt[3])x-1)/2)M.M
t[x_,y_,M_]:=y M.M

zs2[s_,t_,u_,M_]:=((((s(t-u)+(((M[[1]])^2)-((M[[2]])^2))(((M[[3]])^2)-((M[[4]])^2))))^2)/((s-(((M[[1]]+M[[2]]))^2))(s-(((M[[1]]-M[[2]]))^2))(s-(((M[[3]]+M[[4]]))^2))(s-(((M[[3]]-M[[4]]))^2))))
zt2[s_,t_,u_,M_]:=((((t(s-u)+(((M[[1]])^2)-((M[[3]])^2))(((M[[2]])^2)-((M[[4]])^2))))^2)/((t-(((M[[1]]+M[[3]]))^2))(t-(((M[[1]]-M[[3]]))^2))(t-(((M[[4]]+M[[2]]))^2))(t-(((M[[4]]-M[[2]]))^2))))
zu2[s_,t_,u_,M_]:=((((u(t-s)+(((M[[1]])^2)-((M[[4]])^2))(((M[[2]])^2)-((M[[3]])^2))))^2)/((u-(((M[[1]]+M[[4]]))^2))(u-(((M[[1]]-M[[4]]))^2))(u-(((M[[2]]+M[[3]]))^2))(u-(((M[[2]]-M[[3]]))^2))))
sthmax[M_]:=Max[(((M[[1]]+M[[2]]))^2),(((M[[3]]+M[[4]]))^2)]
tthmax[M_]:=Max[(((M[[1]]+M[[3]]))^2),(((M[[2]]+M[[4]]))^2)]
uthmax[M_]:=Max[(((M[[1]]+M[[4]]))^2),(((M[[3]]+M[[2]]))^2)]
sthmin[M_]:=Min[(((M[[1]]+M[[2]]))^2),(((M[[3]]+M[[4]]))^2)]
tthmin[M_]:=Min[(((M[[1]]+M[[3]]))^2),(((M[[2]]+M[[4]]))^2)]
uthmin[M_]:=Min[(((M[[1]]+M[[4]]))^2),(((M[[3]]+M[[2]]))^2)]

Manipulate[Module[{M={M1,M2,M3,M4}},Show[Plot[{(Sqrt[3])(1/(Sqrt[3])+x),(Sqrt[3])(1/(Sqrt[3])-x)},{x,-3,3},AspectRatio->1,PlotRange->{{-3,3},{-3,3}},PlotStyle->{Black,Black},ImageSize->600],RegionPlot[0≤ zs2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1&&s[x,y,M]≥sthmax[M],{x,-3,3},{y,-3,3},AspectRatio->1,PlotRange->{{-3,3},{-3,3}},PlotStyle->Red],
RegionPlot[0≤ zt2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1&&t[x,y,M]≥tthmax[M],{x,-3,3},{y,-3,3},AspectRatio->1,PlotRange->{{-3,3},{-3,3}},PlotStyle->Red],
RegionPlot[0≤ zu2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1&&u[x,y,M]≥uthmax[M],{x,-3,3},{y,-3,3},AspectRatio->1,PlotRange->{{-3,3},{-3,3}},PlotStyle->Red],
RegionPlot[(0≤ zs2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1)&&(0≤ zt2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1)&&(0≤ zu2[s[x,y,M],t[x,y,M],u[x,y,M],M]≤ 1)&& sthmin[M]≤ s[x,y,M]≤Max[(((M[[1]]-M[[2]]))^2),(((M[[3]]-M[[4]]))^2)],{x,-1,1},{y,-1,1},AspectRatio->1,PlotRange->{{-1,1},{-1,1}},PlotStyle->Red]]],
{{M1,1},0,5},{{M2,1},0,5},{{M3,1},0,5},{{M4,1},0,5}]