Class D inductor current calculation
You have a couple of false premises in your question.

First of all, the inductor only needs to handle the peak current, not the peak-to-peak current. The peak current is 14A, since the sign doesn't matter.

Second, you only need one inductor per speaker, even in an H-bridge configuration.

Finally, if your power supply to the H-bridge is only 20V, then the peak voltage you'll be able to generate across the load is exactly that &mdash; 20V. The peak-to-peak voltage will be 40V and the sinewave RMS voltage wil be 14V. The maximum sinewave power into 4&Omega; will be 50W. The peak current will be 5A and the RMS current will be 3.54A.

If you really want to develop 40 Vrms across your 4&Omega; speaker, you'll need a supply of at least 60V to the H-bridge.