(no subject)
1. SO WE HAVE CRUSNIK, METHUSELAH (BACILLUS) AND TERRANS, RIGHT.
2. ... I don't think the fertility rate goes down as fast with age in Methuselah or Crusnik. Since the series is all '|D hurr only 50 years old? YOU VAMPIRE WHELP CHILD thingy.'
3. Crusnik nanomachines won't do anything to Terrans, since they can't live on Terran blood -- but if a Crusnik's nanomachines aren't activated, then his/her bodily fluids won't hurt a Methuselah either.
(I say this because Abel's blood doesn't eat vampires every time they impale him. And they impale him a lot.
That was not a euphemism.)
4. ... if a Methuselah gets literally Crusnikraped it's DEATH BY SPERM. Ew.
5. Methuselah/Terran intercourse is possible (Unless it's directly blood/blood, Bacillus is less, er, reactive???) but canonically taboo, probably because of the next point:
6. On pregnancy:
a) METHUSELAH father + TERRAN mother / CRUSNIK father + METHUSELAH mother = mother dies from baby being a parasite.
b) TERRAN father + METHUSELAH mother / METHUSELAH father + CRUSNIK mother = ... potential baby gets reabsorbed quickly.
c) TERRAN/CRUSNIK baby would probably have all sort of complications if the nanomachines activated at any time during the pregnancy, and a Terran mother would probably die from the effects. O-ow CLAWS IN THE UTERUS.
... the Crusnik bits are mostly conjecture since none of the siblings are trying to have kids anyway, uh. But we never ever see half-breeds in TB canon and THAT MIGHT BE WHY.