Short answer:

• Nami and Vinami are brothers in a Jain narrative. They are both sons of King Kaccha (in Hemachandra’s Triṣaṣṭiśalākāpuruṣacaritra). Bahubali (Gomateshvara) is a different figure: he is the son of Rishabhanatha (Adinath) and belongs to an earlier part of the Tirthankara lineage. So, Nami–Vinami and Bahubali do not have a direct family relation in the standard Jain chronology; they come from different generations in Jain mythic histories. You can read more about Nami and Vinami as brothers here.

Notes:

• If you’re exploring how Naminath (Nami) and Neminath (Nemi) relate in other traditions, some Purāṇa-era texts describe Neminath as connected to Krishna as cousins; this is a narrative motif in Śvetāmbara literature rather than a doctrinal statement about the Tirthankaras. In Digambara texts, the emphasis on such kinship is less central. For context on that Purāṇa style kinship, you can look at related discussions here.