Looking at the decay chain, I saw it undergoes double beta decay. How is it feasible for something to undergo a simultaneous double decay?
The condition for double beta decay to be the preferred mode are that the energy (mass) of the three states
have a relationship like
$$ E_d < E_m < E_s \,.$$
The result is that it is not possible for a single decay to proceed (there is not enough energy) but it is possible for a double decay to happen (though it will be a slow process).