At an energy harvesting relay, securing residual harvested energy, net remaining energy after each receiving and forwarding cycle, is of importance for sustainable operation. However, there exists a tradeoff between the achievable rate and residual harvested energy, whereby understanding this tradeoff concretely is crucial for energy harvesting relay system design. This paper analyzes the rate-energy (R-E) region for achievable rate and residual harvested energy in two-way decode-and forward (DF) relay systems with a power splitting based energy harvesting relay. In particular, we characterize R-E regions for multiple access broadcast (MABC) and time division broadcast protocols. Moreover, we propose a new energy harvesting relaying protocol, namely, information and energy signals multiple access broadcasts (IEBC), to improve the achievable R-E region. The boundary of the R-E regions is obtained by optimizing a power splitting factor in each protocol. Moreover, to have better analytic comparisons and useful insights on performance, we derive approximated R-E regions of all protocols for high and low signal-to-noise ratio cases. Based on the approximated R-E region, it is shown that if the required residual energy is large, the IEBC outperforms the others, but if the required residual energy is small, either the IEBC or MABC is preferred.