Re: Draupadī and Dhṛṣṭadyumna
Similarly, in Mahabharata, we read about Draupadi and Dhristadyumna, who are also ayOnijas, borne out of fire.
That's what the Mahābhārata initially tells us. In fact, we are told that a youth and a young maiden arose from the fire altar. Unlike Sītā's case, these are not babies. Most likely they were teenagers.
Ādi Parva - Ch. 155
Then a youth [Dhṛṣṭadyumna] who resembled a god arose from the flames. His
complexion was like the fire and his form was terrible. He wore a
crown on his head and his body was encased in excellent
armour. He had a sword in his hand and a bow and arrows and
he let out many loud roars. As soon as he was born, he ascended
a supreme chariot and went forth...
Then a young maiden [Draupadī] arose from the centre of the altar. She was blessed with good fortune and was known as Panchali. She was beautiful and
her waist was shaped like an altar. She was dark. Her eyes were
like the petals of lotuses. Her hair was dark blue and curled. She
was truly a goddess born in human form. The sweet fragrance of
blue lotuses emanated from her body, a full 2 miles away. Her
form and supreme beauty were such that she had no equal on
earth. When the one with beautiful hips was born, the invisible
Supreme among women, this beauty of the dark
complexion will bring about the destruction of the Kshatriyas. In
time, this one with the beautiful waist will perform the objective
of the gods. From her will arise terrible fear among the
Debroy, Bibek. The Mahabharata: Volume 1 (pp. 401-402)
However, we are also told later that Draupadī had a very normal childhood with Dhṛṣṭadyumna and her other brothers:
Vana Parva - Ch. 33
O Partha! I have not insulted or censured
dharma in any way. Why should I censure the supreme god, the
lord of all beings? O descendant of the Bharata lineage! Know
me as one who is incoherent with grief. Listen to me with a calm
mind, as I lament a lot more. O destroyer of enemies! Whatever
is born must certainly perform tasks. Not even inferior ones, but
only the immobile can live without acting. O Yudhishthira!
From the time one suckles at a breast to the time one is supine
before death, all mobile beings act according to their nature.
O Yudhishthira! He should wish for his misery and destruction. This is true of oceans and mountains, not to speak of mortal men. By looking for the weaknesses in an enemy, a man satisfies a debt to himself, as well as to the enemy. A man should never think ill of himself. O descendant of the Bharata lineage! Prosperity does not come to one who thinks of himself as having become overpowered.
O descendant of the Bharata lineage! This is the foundation for the success of the world. It is said that the reasons for success are many and depend on the time and the place.
In earlier times, a learned brahmana was lodged in my
father's house. O bull among the Bharata lineage! He told all
this, first propounded by Brihaspati, to my father. He also
taught all this to my brothers. I overheard this conversation at
home. O King Yudhishthira! He explained this to me
comfortingly, when I would arrive on some task, or when I was
serving, or when I was seated on my father's lap.
Debroy, Bibek. The Mahabharata: Volume 2 (pp. 360-364)
If Draupadī and Dhṛṣṭadyumna were already teenagers when Drupada first found them, how was Draupadī able to give the above discourse on dharma to Yudhiṣṭhira? Where was the time to learn all the intricacies of dharma from her father and the brāhmaṇa guru?
Also, earlier in Ādi-parva (Ch. 155), when Draupadī and Dhṛṣṭadyumna rise up from the fire, Drupada's wife Pṛṣatī makes a special request:
On seeing these two, Prishati wished to get them and came to Yaja and said,
Let these two know no one but me as their mother.
Desiring to please the king, Yaja agreed. The Brahmanas, whose desires were entirely satisfied, gave the two names.
Because of his great courage and because he has been born from lustre, let this son of Drupada be called Dhrishtadyumna. Because she is dark in complexion, let her be called Krishna.
Drupada doesn't make the same request. This suggests Drupada could have fathered the two children from another woman and now Pṛṣatī is requesting the priests for a formal adoption.
So, instead of speculating on the technology of miraculous births of those times, you should be asking:
Why did Drupada cover up the fact that he had children with his legal wife Pṛṣatī or another woman until they were teenagers?
And what was the need to conduct a yajña to introduce them to the whole world?