The devas are respected by performance of fire sacrifices and so on. Fathers and mothers are respected by obeying their instructions and menially serving them.

In some manuscripts, bhṛtyān appears instead of mātṝḥ indicating that one should respect one’s servants by giving them charity, by allowing them to serve [their] superiors and so on.

Those equal to one’s father, that is, relatives equal to one’s father should be respected by giving them wealth in charity. The elderly and so on should be offered respectful obeisances and so on. “Elderly” refers to those elder by knowledge, character and age. Vaidyāṁś ca brāhmaṇāṁś ca can also indicate that physicians should be respected by gifting them with wealth and so on, and that the brāhmaṇas [should also be respected].

NOTE. Regarding respecting brāhmaṇas, Śrīla Prabhupāda has noted the following in his commentary to Caitanya-caritāmṛta (Ādi 17.9):

When Śrī Caitanya Mahāprabhu went to Gayā,  accompanied by many of His disciples, He became sick on the way. He had such a high fever that He asked His students to bring water that had washed the feet of brāhmaṇas, and when they brought it the Lord drank it and was cured. Therefore everyone should respect the position of a brāhmaṇa, as indicated by Śrī Caitanya Mahāprabhu. Neither the Lord nor His followers displayed any disrespect to brāhmaṇas.

The followers of the Lord must be prepared to offer brāhmaṇas all due respect. But preachers of Lord Caitanya’s cult object if someone presents himself as a brāhmaṇa without having the necessary qualifications. The followers of Lord Caitanya cannot blindly accept that everyone born in a brāhmaṇa family is a brāhmaṇa. Therefore one should not indiscriminately follow the Lord’s example of showing respect to brāhmaṇas by drinking water that has washed their feet. Gradually the brāhmaṇa families have become degraded because of the contamination of Kali-yuga. Thus they misguide people by exploiting their sentiments.