As my distant memory from DOS 2 abandons me, question, are there "half-xxxx" "races" or similar in the Divinity universe, like f.e. in DnD?
I cannot recall, nor find any information about mixed races. Besides Malady who's half-demon (And a total mommy

) though it's not made clear if this is a result of relations, magic or possession (As we also see with Lohse).
It certainly wouldn't make much sense for them to exist based on real life logic. Given that the 6 main races were created completely separately. While in real life mixed breeds only exist between very closely related species (And end up sterile meaning their population is always exceedingly low).
As far as using inter-racial relations as a means of contraception... It could happen. Such a thing is never really explored too much. Though one could also assume magical contraceptives could exist, as well as Ye Olde contraceptives (I.e. Cloth condoms which were used back in history)