You would put them in the following order:
a, |b-c|, |a-b|, |a-c|
In order to find the values of these in the appropriate values, you can use just about any number that the point falls between. For our sake we'll use a = -3.9, b = -1.1, and c = -0.9.
a is obviously the smallest as it is negative and the rest are absolute values. A absolute value cannot be negative, so they all must be greater than a. After that you can evaluate the other 3 and see a clear order.
|b - c|
|-1.1 - -0.9|
|-.2|
.2
|a - b|
|-3.9 - - 1.1|
|-2.8|
2.8
|a - c|
|-3.9 - -0.9|
|-3|
3
This sets a fairly clear order between the 3 as -3.9, .2, 2.8, 3. Also, even if you change the numbers slightly, these will always be the order.
