Just from what you said, it appears that you are capable of defeating them and advance, but just not enough to hold the ground. I would definitely not advice you to split troops and land another front unless you have numerical superiority, otherwise it will just put more strain on your TC as well as wasting away valuable troops.
My suggestion is to fall back a bit and create some kill zone buffer. Make sure you have several provinces enveloping the buffer zone, preferably without river crossings. Now attack any troops that cross into that buffer zone, use 1 unit to attack with the rest on support attack. Make sure you have some 1-unit stacks waiting so you can keep pounding on incoming enemy while the 1st unit reorganizes. Since you should have overwhelming advantage, you will lose less troops and organization. Do this for a few months and the Germans will likely draw troops from nearby provinces to fill in this "hole". Once the line is this enough, order your elite troops to break a hole in the thinned line and advance. When you are trying to break through, make sure to check the synchornize arrival box or else your troops are going to get picked off one by one by the enemy just like what you did to the buffer zone.
