So from what I've read, Ymir was essentially the father of the frost-giants, the Jötunn, but there were other giants such as Gymir/Ægir who are sea-giants, Surt the leader of the fire-giants, and Aurboda who is a mountain-giant, and they also resided in Jötunheimr (minus Surtr) and are considered Jötunn. Is Jötunn just a direct translation of Giant? If so, how did it get turned into frost-giant when referring to the Jötunn that came from Ymir? Are the other types of giants still the direct descendants of Ymir, or did they come from the frost-giants themselves?
Other Questions
So I'm currently working on a poster about Norse Mythology, with a focus on a sort of "family-tree". These are few things of I can't make my mind up about and I'd love some help so I can figure out how to organise the information.
1. Are the nine daughters of Ægir also the nine mothers of Heimdall? If so, wouldn't that make Heimdall a giant, because both of his grandparents are? Does the fact that he isn't a giant alone mean that this can't be the case? Should the fact that the nine daughters and the nine mothers have different names be taken into account, even though this seems to only be referred to in the one poem (Lay of Hyndla)?
2. Sköll and Hati chased the Sun and the Moon, but who chased which? Snorri says Sköll chased the Sun and Hati the Moon, but Snorri's source suggests the opposite (see here), and I'm not sure which to go with.
I am very confused by all of this and can easily see how someone can spend their whole life studying this stuff. I'm sure I'll have more questions soon.
Also, if anyone with knowledge on this subject would be willing to proof-read what I've got so far it'd be awesome if you could PM me. I'm also working on a Greek and Ancient Egyptian version if anyone with knowledge on those would be willing to help out
You might do well to ask /r/Norse for help since there are many people there who are well versed in this material, and someone may be willing to proofread your work.
That said, please keep in mind that sources for Norse mythology were generally written long after conversion, and their view of a past culture was necessarily seen through a fogged lens. Contradictions and lack of a definitive version can be credited to this problem with the sources, but it is also important to remember that folklorists working with pre-industrial European peasants observed that the folk often provided contradictory stories about the supernatural, and their descriptions of these beings could be vague with blended boundaries between various entities that we might prefer to see as clearly defined and distinct.