As ISKCON's Governing Body Commission (GBC) clarified recently while appointing female dīkṣā gurus, they rely on the teachings of Swami Prabhupada and Chaitanya Mahaprabhu and not that of Ramanujacharya:
The primary bases for this decision are the expressed desires and instructions on guru qualifications of ISKCON's Founder-acarya His Divine Grace Srila A.C. Bhaktivedanta Swami Prabhupada.
We recognize that some members and friends of ISKCON may object to this resolution based on their own reading of sastra, their own social experiences, or deeply held Vaisnava convictions.
In the meantime, we humbly request ISKCON devotees to see this resolution in the light of the inclusiveness of Lord Chaitanya and our previous acaryas, and as facilitating senior, mature and exemplary followers of Srila Prabhupada in their dedicated service to him and his ISKCON. Please bless them in this new important spiritual responsibility.
So one who is spreading krsna-upadesa, simply repeat what is said by Krsna, then you become acarya. (...) Suppose you have got now ten thousand. We shall expand to hundred thousand. That is required. Then hundred thousand to million, and million to ten million. So there will be no scarcity of acarya, and people will understand Krsna consciousness very easily.
(Lecture on Sri Caitanya-caritamrta, Adi-lila 1.13 – April 6, 1975, Mayapur)
As for upanayana or brāhmaṇa initiation performed for "śūdra" and "mleccha" disciples, this is what Prabhupada has stated:
Similarly, a disciple's qualifications must be observed by the spiritual master before he is accepted as a disciple. In our Kṛṣṇa consciousness movement, the requirement is that one must be prepared to give up the four pillars of sinful life — illicit sex, meat-eating, intoxication and gambling. In Western countries especially, we first observe whether a potential disciple is prepared to follow the regulative principles. Then he is given the name of a Vaiṣṇava servant and initiated to chant the Hare Kṛṣṇa mahā-mantra, at least sixteen rounds daily. In this way the disciple renders devotional service under the guidance of the spiritual master or his representative for at least six months to a year. He is then recommended for a second initiation, during which a sacred thread is offered and the disciple is accepted as a bona fide brāhmaṇa. Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura introduced the system of giving the sacred thread to a bona fide Vaiṣṇava, and we are following in his footsteps.
The qualifications of a bona fide disciple are described in Śrīmad-Bhāgavatam (11.10.6) as follows:
amānya-matsaro dakṣo nirmamo dṛḍha-sauhṛdaḥ ।
asatvaro ’rtha-jijñāsur anasūyur amogha-vāk ॥ 11.10.6 ॥
The disciple must have the following qualifications. He must give up interest in the material bodily conception. He must give up material lust, anger, greed, illusion, madness and envy. He should be interested only in understanding the science of God, and he should be ready to consider all points in this matter. He should no longer think, “I am this body,” or, “This thing belongs to me.” One must love the spiritual master with unflinching faith, and one must be very steady and fixed. The bona fide disciple should be inquisitive to understand transcendental subject matter. He must not search out faults among good qualities, and he should no longer be interested in material topics. His only interest should be Kṛṣṇa, the Supreme Personality of Godhead.
He states the same in a letter dated January 23, 1974:
We are criticizing the caste brahmanas for saying that the Americans and Europeans cannot be awarded brahmana initiation, because according to Vedic sastra, anyone who is properly trained up under a bonafide spiritual master, can become twice born.