These three Goddesses are celebrated together in all the āpri hymns namely: 1.13.9; 1.142.9; 1.188.8; 2.3.8; 3.4.8; 5.5.8; 7.2.8; 9.5.8; 10.70.8; 10.110.8; Note that Mahī and Bhāratī are same. We reproduce below the comments of Sri Kapāli Sāstry.
The purāņās speak of no difference between Bhāratī and Sarasvatī. According to the purāņic story, Iļā, male head of the lunar dynasty, son of Manu, attained womanhood and became Iļā. But in the Veda, it is to be noted, these three associated together, conferring Sight, Hearing Vastness on the sacrificer, the rişhi, have their dwelling in Svar. Of these, Bhāratī signified by the term Mahī, the divine Power connected with the Vast Light, issuing from the House of svar, brings first the consciousness of the vast, bŗhat, to the Seer-Poet; Iļā favours him with the consciousness-sight, commensurate with this vastness. But Sarasvatī, the carrier of inspiration makes the seer capable of hearing the divine inspiration, the hearer of Truth.
The truth of Bhāratī or Mahī is described in (1.8.8) with the three adjectives sūnŗta, one with true speech, virapshī, flowing abundantly, and gomatī, full of the rays of Light. The entire hymn (1.8) entitled “Indra and Mahī” will be discussed in the second volume. Even though sūnŗta is used for Sarasvatī also in (1.3.11), we have to grasp the distinction between the deities.
Iļā, Sarasvatī and Bhāratī, conferring Sight, Hearing and Vastness respectively, are divine, born of the Truth-Light, powers of the Sun of the Light of Truth impeller supreme of the Universe. The adjective vishvatūrtiĥ (who carries all) used for Her of the Vastness, establishes the relation of Bhāratī to the very Impeller who is sought to impel our thoughts. All these three create supreme happiness-mayobhuvaĥ. They are not to be taken as some indistinct or formless divine powers; though they are mutually associated, the seers see their form as distinct, beautiful, supeshasaĥ, of good form.
We give below translations of some of the āpri mantrās.
May Iļā, Sarasvatī, Mahī, the three Goddesses of delight come to the seat, unharmed (1.13.9).
May Sarasvatī affecting our thought dhiyam and Goddesses Iļā and Bhāratī who carry all to their goal sit on our altar seat and guard our house of refuge by the self-law of things svadhaya. (2.3.8)
In unison may Bhāratī with her muses of invocation bhāratibhih, Iļā with gods, men and Agni, Sarasvatī with her powers of inspiration sārasvatebhirvāk, come down to us; may the three goddesses be seated, (7.2.8) and (3.4.8).
May Iļā, Sarasvatīī and Mahī, the three Goddesses who create the bliss sit on the sacred seat, they who never err (5.5.8).
May Bhāratī come swiftly to our sacrifice, Iļā awakening to knowledge like a human thinker and Sarasvatī, the three Goddesses, –may they sit, perfect in works, on this sacred seat of happy ease (10.110.8).
O ye three Goddesses, sit on the superior seat which we have made delightful for you; may the mother of revelation, Iļā, and the two goddesses with the luminous feet, ghŗtapadī, accept our firmly placed offerings and our human worship of sacrifice (10.70.8).
The translations are all due to Sri Aurobindo (HMF). Note in (10.70.8), the usual translation of ghŗtapadī as having feet of ghee does not make sense.