Yeah, in all honesty the only Lala halfbreeds would probably have the Lala as the father far more often than not. The mothers are just too bloody small to the point where even their own children are an unreasonably large proportion of their size (especially considering their heads).
That being said... no, Roegadyns being physically large does not necessarily mean their penis size scales in proportion to their bodies. Gorillas have notoriously small penises, for example, relative to their body mass (1.5 inches!). It could very well be that they are no larger there than an ordinary human being. I would still recommend she not attempt to sire children regardless...
(Also, there is porn of this)
That being said... no, Roegadyns being physically large does not necessarily mean their penis size scales in proportion to their bodies. Gorillas have notoriously small penises, for example, relative to their body mass (1.5 inches!). It could very well be that they are no larger there than an ordinary human being. I would still recommend she not attempt to sire children regardless...
(Also, there is porn of this)