Maybe you want to nest two Manipulate expressions here?
group1[x_] := Manipulate[x, {x, 0, 1}];
group2[x_, y_] := Manipulate[{x, y}, {x, 0, 1}, {y, 0, 1}];
group3[x_, y_, z_] := Manipulate[{x, y, z}, {x, 0, 1}, {y, 0, 1}, {z, 0, 1}];
Manipulate[group, {
{group, group1[x], "Select group"},
{group1[x] -> "group1", group2[x, y] -> "group2", group3[x, y, z] -> "group3"}
}]
Or with a TabView:
TabView[{"group1" -> group1[x], "group2" -> group2[x, y], "group3" -> group3[x, y, z]}]