Okay...more on the fascinating world of 'Sex and Childbearing'.
Elf/Olca is impossible without a great deal of dark sorcery aka 'science'.
Elf/human offspring are possible, but only out of human females. They cannot be sired by humans.
The birth mother connection is that Elves reproduce very rarely (logical in an immortal species) and this is entirely controlled by the females. (Their gestation is approximately the same as humans, though--a trade-off between their rapid cell growth and the need for additional development. They are a lot more 'aware' when they are born).
A She-elf will bear children only of the one with whom she is destined to bear them. Gaelen and Rain 'recognized' one another at/near the very end of his life, regrettably (for him). They might, of course, enjoy the (ahem) pleasant company of anyone, but once they recognize their life-mate they are bonded for eternity. Part of Gaelen will always turn to Rain, and Orogond knows it, but he doesn't care. She loves him to the limit of her ability and that is enough for him.
Elven males can (and do) freely sire children of human females--there are no biological constraints. However, it is unlikely that they will do so because of behavioral/cultural/social mores. It IS considered unseemly. Those mores came out of the realization that loving a human results in endless heartache upon separation (ask Galador). And the Elves cannot deny their (fairly pervasive) snobbery, either! Some Elves, like Galador and Gaelen, truly appreciate and admire humans. They are not in the majority. Wood-elves don't disparage humans to the degree that High-elves do, but Wood-elves tend to be suspicious of everybody.
As far as Dwarves are concerned, talk about social constraints!! Their 'reproductive biology' is revealed in the next book, and I will speak no more of it for the moment. Biologically, they are (relatively) compatible with (male) Elves and with humans, but there might be mechanical difficulties due to size differences. Offspring are unheard of (at least in the West), but if they appeared, they would be sterile.