For completing the energy transition, ordinary citizens have to be able to participate. This can be achieved with energy communities (ECs), which are getting implemented into law in EU member states. However, some of these legislations do not account for the possible challenges of implementing ECs. One such example is Austrian law, which - in an attempt to take citizen involvement one step further - will allow for simultaneous participation in multiple ECs. However, the law does not state how energy should be distributed among these communities, which opens the door to ambiguities that could lead to not being able to process their energy allocation. The aim of this paper is to analyze different methods of energy allocation between communities and their members when there is multiple participation. Four algorithms are established and tested on solvability, complexity, comprehensibility, and fairness. Only one has proven successful in all categories: distributed demand/production. Here, a preprocessing stage is included, in which each member must declare what percentage of consumption/generation goes to the multiple communities in which they participate. Therefore, energy allocation in all communities may be done in parallel with no dependencies. The result of this paper recommends this algorithm for further regulation of multiple participation in energy communities.