I know they are daedra ofcourse, but they look very human. Can they bear offspring from mortals? Is it possible for one to reason and not be hostile? Can they be considered a race? They are very mysterious and I cant find too much lore on them.

They are daedra. They do not "breed", for there is no point. Death is an inconvenience to them; their spirit just drifts the void until it finds some way to reform. That's why most non-Princely daedra swear fealty to a Prince: the Princes have means to expedite the matter of reformation. Dremora can be reasoned with, as they are one of the greater daedric races and have a higher intellectual capacity. However, odds are someone's still gonna get sliced, as they are still Dremora. Well, maybe not the Dremora sworn to Sanguine, maybe, but definitely Dagon's bunch.

If they cannot "breed" then how are they "born"?

"magic"

They are basically deamons. Presumably the princes can create them, which is... magic...

They aren't born; each individual has always existed as some form of daedra. Dremora are either lesser spirits that aligned themselves with a Principality after creation instead of fleeing alongside Magnus, or are fragmented pieces of Dagon himself, like dragons are to Akatosh. The latter seems more unlikely as that would require a Daedra creating, which they are said to be unable to do.

They are a race, and are just as sentient as the mortal races of man and mer, with an intelligence to boot. They have their own culture, and they have their own sets of laws that distinguish them from other daedra.

They aren't "born." At least, not in the normal way. They've always existed. How they first came to be, is a matter of debate. But there is likely only one generation of them.

That only applies to the mortal plane. In Oblivion they can create to their heart's content.

There is nothing in game, that I am aware of, suggesting a Dremora/Non-Dremora or a Dremora/Dremora mating has ever occurred in the Elder Scrolls universe, but that doesn't mean that those can't happen. The do have the same body parts below the neck.

Regarding hostility: There is a misconception that hostile reaction is based on race, it isn't. It is based on factions and faction reactions. The player character can have a non-hostile interaction with Kathutet in The Elder Scrolls IV Oblivion.

In the Creation Kit, Dremora are considered a race. If you try looking up definitions online, you are probably going to find they are human centered which if used would also lock out any of the Mer from being considered races. Any rational, unbiased, definition of "race" that brings in the Altmer, Bosmer, and etc would have to allow the (sapient) Lesser Daedra in as races.

Be careful about the "lore books" as they are unreliable by design.