Śrī Gaura-Nitāi are considered Viṣṇu-tattva in the Gauḍīya Vaiṣṇava tradition.
Śrī Caitanya Mahāprabhu (Gaura) is Kṛṣṇa Himself, appearing as a devotee to teach and distribute prema-bhakti, especially through the chanting of the holy name.
Śrī Nityānanda Prabhu (Nitāi) is the original Balarāma, who is also Viṣṇu-tattva and the first expansion of Kṛṣṇa.
Therefore, Gaura-Nitāi are not ordinary living beings (jīva-tattva) or demigods; They are Viṣṇu-tattva and are worshipped accordingly.
Śrī Caitanya Mahāprabhu (Gaura) is Kṛṣṇa Himself, appearing as a devotee to teach and distribute prema-bhakti, especially through the chanting of the holy name.
Śrī Nityānanda Prabhu (Nitāi) is the original Balarāma, who is also Viṣṇu-tattva and the first expansion of Kṛṣṇa.
Therefore, Gaura-Nitāi are not ordinary living beings (jīva-tattva) or demigods; They are Viṣṇu-tattva and are worshipped accordingly.
So Gaura-Nitāi can and should be offered Tulasī leaves. A useful principle for Deity worship is that Tulasī is offered to Viṣṇu-tattva forms of the Lord. So in home worship, it is appropriate to offer Tulasī to Gaura-Nitāi, as well as to Rādhā-Kṛṣṇa and other Viṣṇu-tattva Deities.
This is my understanding. Hare Krsna