  We investigate even-even two-proton borromean systems at prominent
intermediate heavy waiting points for the rapid proton capture process. The
most likely single-particle levels are used to calculate three-body energy and
structure as a function of proton-core resonance energy. We establish a linear
dependence between two- and three-body energies with the same slope, but the
absolute value slightly dependent on partial wave structure. Using these
relations we predict low-lying excited states in the isotones following the
critical waiting points. The capture rate for producing a borromean bound state
is described both based on a full three-body calculation and on a very simple
analytic rate expression for temperatures about $1-5$~GK. This rate is valid
for both direct and sequential capture paths, and it only depends on the
three-body resonance energy. As a result the relevant path of the radiative
capture reactions can be determined. We present numerical results for $E1$ and
$E2$ photon emission, and discuss occurrence preferences in general as well as
relative sizes of these most likely processes. Finally, we present narrow
estimated intervals for the proton capture rates relevant for the critical
waiting points.
