Is it normal for a dog to do this?

While some कुत्ता are less या और likely to do it than others, I believe this is a common habit amongst कुत्ता to hump their own पिल्लें या other strange 'partners'-they have been known to do this with stuffed animals, siblings and even people...I am not 100% sure as to why they do this, but I believe it is a habit stemmed from curiosity, with some कुत्ता being और prone to it than others depending on how randy they are द्वारा nature XD As a matter of interest, is Beast an older dog द्वारा any chance? I heard that senior कुत्ता are also और likely to do it, though it is often simply a दिखाना of dominance rather than anything else. Also if he is only 'mounting' and not anything...else, this is a common play gesture among some कुत्ता (although bearing in mind the pups are much smaller this is not such a good thing).

As for what आप should do with him...well, neutering him will reduce the problem (although neutered कुत्ता may also perform this behaviour). Other than that, try removing him whenever he does it and say 'no' firmly, before distracting him with something else. In the wild, a female wild dog या भेड़िया will drive her partner away as soon as her pups are born, as unlike the mother the male dog rarely feels any attachment towards the pups when first born, and so are और prone to unacceptable behaviour; perhaps आप could keep Beast away from the पिल्लें until they are bigger? द्वारा which time, he might perhaps have gotten used to the पिल्लें and not be so inclined to...you know, and if they are bigger they may be able to stand up for themselves a bit more.

Actually, father/daughter या mother/son matings often turn out fine. It really depends on the कुत्ता involved, if they are carriers for any genetic diseases या not.
Inbreeding can be useful in breeding for specific traits, actually, so it's not always a bad thing. (However a breeder should have a pretty good understanding of genetics so that they know what they're doing before inbreeding.)