Nuclear matrix elements for double positron emisson ( β + β +), positron emission/electron capture ( β +/ EC) and double electron capture (EC/EC) in the 2 νββ decay mode and for β + β + and β +/EC decay in the 0 νββ mode are calculated for the experimentally most promising isotopes58Ni,78Kr,96Ru,106Cd,124Xe,130Ba and136Ce within pn-QRPA. We point out that the matrix element for the 2 νβ +/EC decay differs from the 2 νβ + β + matrix element, an effect not considered previously. For the neutrino accompanied decays our calculation predicts for the β +/EC and the EC/EC mode half lives which are shorter typically by 4 7 orders of magnitude than those for the double positron emission. However, even for the best candidates typical values for 2 νβ +/EC (2 ν EC/EC) are still in the range of ̃1022 (( some) 1021) years. For 0 νββ decay we have calculated all matrix elements relevant for both, the mass mechanism and the right-handed currents for the first time complete. A detailed discussion of the differences between the 0 νβ +β+, the 0 νβ +/EC and 0 νβ - β - decay is given.