Is it possible to split an unresolved peak into two peaks?

Yes, it is possible. Trying the Wave integration algorithm is recommended if you have already optimized global parameters and peaks are still unresolved. It may provide better results. 

If this still does not help, use the Add Positive function, choose the part of the unresolved peak, you want to split off and add the interval markers to the borders of the new peak. Both peaks will be separated by a vertical line now. Including the current peak's maximum in the interval would produce no result.