4 - References

Aahuti
Aahuti is a kind of offering normally used in Yagya. It can be of anything from Ghee (clarified butter through fruit, dry fruits, grains to any dry material. Sometimes this word is used for sacrificing something also, such as "Gandhi gave the Aahuti of his life to bring the independence to India".

Madhuban
The present Mathuraa in UP.

Putrikaa Dharm 
In this type of marriage, parents of the girl take their daughter's son as their own son, even if the parents have their own son(s). Manu did so even though he had his own two sons.

Why Brahma, Vishnu, Mahesh appeared as Atri Rishi's sons?
When Brahma Jee ordered Atri Rishi to create the world, he with Anusooyaa went to Riksh Parvat to do Tapasyaa. There he prayed that whosoever is the Swami of all the three Lok, He may bestow me with the children like Himself. Pleased with their Tapasyaa, Brahmaa, Vishnu and Mahesh all three came there on their Vaahan (ride). Then Atri Muni said - "I bow you and respect you but I, with the desire of children, meditated only for one Shree Hari. Then how come that you three appeared before me?" Hearing this the three Dev laughed and said - "You were meditating for whatever Dev, He is we three. Therefore you will have we our Ansh-Roop three sons and we will expand your lineage." After saying this they went to their Lok. When the time came Brahmas's Ansh (part) appeared as Chandramaa, Vishnu's Ansh appeared as Dattaatreya Jee, and Mahaadev's Ansh appeared as Durvaasaa Rishi in Rishi Atri's house.