Hi,

If i'm getting this right, this is how i go about doing curves :

Select the curve tool you need, create the first curve, when you do the second press and hold C on the keyboard and then press and hold the left mouse button, click on the curve you need it to attach to and move the mouse along it, curve should attach it's self to it, move to the end and let go of C and the mouse button, Done .
The when you need to do the last curve, make the second from last point as normal and then do the C/LM buttons and attach the curve onto the other.

They may be other ways but this is how i do my models.

Hope this helps, any probs, feel free to get back.