S= {[1,0], [1,-1], [5,7], [-1,-8]}; %not the most natural of representations, but if it is what you have...
xy = cell2mat(S(:));
x = xy(:,1);
y = xy(:,2);
Now rewrite your multinomials to be vectorized:
p1 = x.^2 + x.*y + y.^2 - 2;
p2 = x + y + x.*y;
And you can then graph
pointsize = 20;
scatter3(x, y, p1, pointsize, 'r');
hold on
scatter3(x, y, p2, pointsize, 'b');
hold off