They are living harmoniously.

Permaculture (permanent agriculture) is the practical conscious design and maintenance of agriculturally productive ecosystems which have the diversity, stability, and resilience of natural ecosystems. It is the harmonious integration of landscape and people providing their food, energy, shelter, and other material and non-material needs in a sustainable way.

Harmonious spouses can even empty all the water out of the Pacific Ocean.

In a good marriage we can argue harmoniously.

In chess, harmonious coordination of attack and defense forces is of utmost importance.

Tom and Mary live together harmoniously.

They sing harmoniously.

The villa was harmonious with the scenery.

Politicians from Brazil to New Zealand all agreed that culture helps communities live together harmoniously.

Tom and Mary live a harmonious life together.