  We investigate the effect of including a significant ``binary twin''
population (binaries with almost equal mass stars, q = M2/M1 > 0.95) for the
production of double compact objects and some resulting consequences, including
LIGO inspiral rate and some properties of short-hard gamma-ray bursts. We
employ very optimistic assumptions on the twin fraction (50%) among all
binaries, and therefore our calculations place an upper limits on the influence
of twins on double compact object populations. We show that for LIGO the effect
of including twins is relatively minor: although the merger rates does indeed
increase when twins are considered, the rate increase is fairly small (1.5).
Also, chirp mass distribution for double compact objects formed with or without
twins are almost indistinguishable. If double compact object are short-hard GRB
progenitors, including twins in population synthesis calculations does not
alter significantly the earlier rate predictions for the event rate. However,
for one channel of binary evolution, introducing twins more than doubles the
rate of ``very prompt'' NS-NS mergers (time to merger less than 1 Myr) compared
to models with the ``flat'' q distribution. In that case, 70% of all NS-NS
binaries merge within 100 Myr after their formation, indicating a possibility
of a very significant population of ``prompt'' short-hard gamma-ray bursts,
associated with star forming galaxies. We also point out that, independent of
assumptions, fraction of such prompt neutron star mergers is always high,
35--70%. We note that recent observations (e.g., Berger et al.) indicate that
fraction of short-hard GRBs found in young hosts is at least 40% and possibly
even 80%.
