And besides, what of the people of Dor-lomin that rebelled against Brodda at the sight of Turin? It is said that they hid in the mountains, waiting for Turin to come back and save them, but Turin never went back, for he died in Brethil, so what happened to the people of Dor-lomin?
And how exactly was Aerin related to Hurin? She is said to be Indor's daughter, but who is Indor?
Tolkien would've surely mentioned it if they were siblings.
Though I guess that much is already known
Indor might've been a brother of Galdor
I don't think this is the case, as Galdor's only siblings were Gundor and Glóredhel. I don't believe Indor's relation to Hurin is ever mentioned.
I don't think this is the case, as Galdor's only siblings were Gundor and Glóredhel.
According to what?
Tolkien juggled with family ties quite a lot.
With respect to textual references outside tables: 'The sons of Hador were Galdor and Gundor; and the sons of Galdor...' (Later Quenta Silmarillion). If these were the only sons then 'Indor' would have to be female to be another sibling of Galdor, which would not fit very well given other considerations.
Certainly Tolkien was not against revision in general, but in any case this is in response to the 'according to what' part.
Just to note it, the name had been used much earlier (starting in The Book of Lost Tales) for the 'father of Tuor's father', and was said to be perhaps the word indor 'master (of house) lord' used as a proper name (the words indo 'house' and Gnomish ind, indos 'house, hall' are noted in this very early context).