The antim samskara (funeral rites) of Ravana's body was performed by Vibishana.
After the death of Ravana in war with Rama. Rama asks Vibishana to perform funeral rites to Ravana's body
In the meanwhile, Rama spoke to Vibhishana as follows: "Let the
obsequies of your brother be performed and let these crews of women be
Yes Ravana killed his sister's husband.
As per this chapter of Valmiki Ramayana: Uttar Kanda:
And then going to the city named Asma ruled by the Kalakayas, Ravana() slew the Kalakayas endowed with terriffic striength ;and then with his sword cut of his brother.in law, the husband of Surpanakha, the mighty Vidyujjihva possessed of terriffic strength; as that ...
There is no evidence of an encounter with Dasharatha
The claim of Dasharatha defeating Ravana comes from this fictional book: History of the Earth
This is what Dasharatha tells people about Ravana in the actual ramayana :
Thus when he is said so by that sage Vishvamitra, then the king Dasharatha spoke to the sage, "I myself am not capable of standing ...
Kumbhakarna was cursed by Lord Brahma. This story is told by Vibhisana to Lord Rama in this chapter of Yuddha Kanda of Valmiki Ramayana. In summary what happens is:
Kumbhakarna soon after his birth begins to eat thousands of living creatures.
Lord Indra was reported about this matter and he goes to punish Kumbhakarna.
Kumbhakarna plucks tusk of Airavata and ...
Hanuman killed Nikumbha
Then, while the roaring Nikumbha was killed in battle by Hanuma, there ensued an exceedingly terrific struggle between the enraged Rama and Makaraksha, son of Khara a ruler of demons.
Sugreeva Killed Virupaksha(son of ravan)
Beholding that mighty Virupaksha ...
The first story can be found in Valmiki Ramayana: Uttara Kand: Sarga 31. After that incident, Kubera's son Nalakuvera cursed Ravana:
[Nalakuvera said:] O fair one [Rambha], since thou hast been ravished by him [Ravana] despite thy unwillingness he shall never be able to get by an unwilling damsel. Whenever he shall, stricken by lust, ravish a reluctant ...
Traditions differ from one kingdom/area to another.
Vanaras follow a tradition of marrying wife of dead brother. That was why Sugriva married Tara, after the death of Vali.
On reaching Kishkinda, in Pushpaka Vimana, Sita says as follows;
सुग्रीवप्रियभार्याभिस्ताराप्रमुखातो नृप || ६-१२३-२४ अन्येषां
वानरेन्द्राणां स्त्रीभिः परिवृता ह्यहम् | गन्तुमि...
In Vālmīki Rāmāyaṇa, the only time Paraśurāma (a.k.a Rāma Jāmadagnya) ever appears in person is when he confronts Rāma Dāśarathi in Bāla Kāṇḍa, sargas 72-75 of the critical edition.
Bāla Kāṇḍa (Sarga 75)
The handsome Rama, Dasharatha's son, released the supreme arrow. The darkness was dispelled and all the directions could be seen. ...