According to Tattvārtha Sūtra, a soul in Deva gati is not alone.

• Devalok is a realm where many devas and devis reside.
• Each deva/devi is an individual jīva with its own body and own karmic state.
• They do not share one body or one soul.
• They may live in the same heavenly region / vimāna / devalok, but each remains separate.

So the correct Jain understanding is:

Many devas and devis exist in Devalok, and each soul is independent. You are not alone there, but you are also not “shared” with others.

In Jain terms, a soul never merges into a collective identity; every jīva remains distinct according to its karma.