Thank you for your replies. I have done the vampire quest on several characters but didn't view that as Molag Bal "falling for" Lamae, at least not in the sense that I meant it. It's a good point to make, though, in that it does seem that Daedra have only "negative and primal emotions." And so Lamae isn't half-daedra; she became the Blood Matron. Hm, I guess there's nothing (in-game at least) that would lead someone to the conclusion that there could exist a being that is Half Daedra/Half Elf or Half Daedra/Half Human, Orc or what have you. Stibbons's seed notwithstanding, it could, admittedly, be interesting. I wonder if he finally succumbs? haha...
Daedra see all Mortals as lesser beings. Their favorite things to do is torture and kill Mortals, so i kinda doubt it.
So generally, while something like Daedric sex may have happened now and then, I'd be generally a bit skeptical when it comes to claims like that. Making up entire genealogies of divine and half-divine beings (and claiming divine ancestry for themselves or their kings) has been a favourite pastime of humanity for millennia, and it's probably the same in Tamriel.
"Granny, where do vampires come from?" "Well, you know, there once was a beautiful maiden..." is, I think, the more likely origin of that Molag Bal - Lamae story.
It is possible for Daedra to procreate (see Molag Grunda, the product of a union between Molag Bal and Azura), though the only recorded instance of a Daedra procreating with a mortal is the story of the creation of vampires in Tamriel: Molag Bal "profaned" a Nedic virgin, after which he shed a single drop of blood upon her brow; this caused her to pass into undeath, at which point she mutilated the people who tried to help her and turned them into the first vampires. Horror-stricken at what she had done and become, she cursed Molag Bal and attempted to plead with Arkay to take her back (i.e. cure her and forgive her); when Arkay refused, she cursed him. The quest to become a full-fledged vampire here, in ESO, explains all this in detail; it might not hurt to play through it to understand this a bit better (you can cure yourself by talking to a Priest of Arkay afterwards, if all you want to do is experience the story; all he requires is a small donation in gold to promote his and Arkay's good works).
As for actual love... no Daedra has ever been known to show anything but negative and primal emotions, though the aforementioned article on Molag Grunda states that she did have some kind of a relationship with a Frost Atronach, so it may very well be possible that Daedra can feel the same emotions mortals do; this could very well mean that they are not inherently evil... which could lead to some interesting stories...
TL;DR: There is only one recorded union between a Daedra and a mortal (Molag Bal and a Nedic virgin); this union created all the vampires that plague Tamriel, but especially the "pure strain" as seen in ESO. As for the emotion of love, no Daedra has been known to express anything but negative and primitive emotions, though it's not entirely ruled-out, either; it just hasn't been recorded.
If I remember right, Malacath is the corrupted excrement of Trinimac. It was Trinimac was defeated and eaten by... Molag Bal(?), the waste turned to Malacath.
Basic breakdown of Imperial Divine = Altmeri Aedra:
Akatosh = Auriel (Auri-El is generally the spelling preferred by the Falmer (Snow Elves, natives of Skyrim) and Bosmer (Wood Elves, or "Tree-sap Folk" in their translations)
Mara = Mara
Dibella = Dibella
Kynareth = Kynareth ("Kyne" to the Nords)
Stendarr = Stendarr
Julianos = Magnus
Arkay = Arkay
Zenithar = Zenithar
Special note on Talos: He's only worshipped by Imperials and Nords (the Bretons have Ebonarm, while the Redguards have a religion completely different from those in Tamriel, though similarities still exist). Talos was originally a Nord, Breton, or Atmoran (accounts vary) (Atmora is the ancient home of the Nords, far to the north of Tamriel), full name Talos Stormcrown, who sought to conquer all of Tamriel in the 2E 890s. Upon his successful conquest (perhaps during), he took the Imperial name Tiber Septim, founding the Septim Dynasty of Emperors of the Third Era (the Third Era began on the 1st of Morning Star directly after Septim's conquest the year prior, 2E 896). Since this was an empire of Men, the Elves couldn't stand worshipping a human as a god, especially considering that their own religions state that only Elves can attempt to re-achieve apotheosis (Elves in TES claim that they are directly descended from the Gods, whom they call the "Aedra", which means "Ancestor" in Aldmeris, the language of the High Elves).
Note on the creator/trickster/tester god: He's most commonly known as "Lorkhan", which is his Elven name; he's also known as "Shezarr" to the Imperials, and "Shor" to the Nords (not sure what the Bretons call him).
Don't think there's any mixed Daedra-Human/Elf offpspring, there's a bunch of cases of them falling in love(and Daedra being not so loving). There are characters which are said to be daughters or sons of Daedra like Molag Grunda or Fa-Nuit-Henbut they can just as likely be adopted. Most Daedric princes are genderless too which probably adds to the likelihood that they can't procreate.
There are a bunch of instances though where mortals become Daedra like the Hero of Kvatch and I am guessing Umaril the Unfeathered too as well as Aedra turning into Daedra like Meridia and Trinimac but never the other way around.
Interesting. So if mortals and Aedra can become Daedra, can Daedra become Aedra?