Elmer is interfaced in FreeCAD for some features in temperature and electrostatics so I'll answer the question as Elmer developer.
You can basically solve thermo-electric problems using weakly coupled or strongly coupled strategies for temperature T and electric potential phi. For weak coupling you still need non-standard source terms that depend on the gradient of the other term and some iteration among the equations. So whereas you might be able to define part of the case using FreeCAD to setup the case definitely it would be a challenge.
In Elmer there is also a dedicated module that solves for phi and T from a strongly coupled 2x2 system. The advantage is that it does not require any iteration. I think this was implemented for some single user and hence there is not any documentation. But if you can start from knowing that the module is ThermoElectricSolver.F90 and the only consistency case for it is called ThermoElectric then you might give Elmer a try. FreeCAD could still be used to define the mesh.
https://github.com/ElmerCSC/elmerfem/bl ... Solver.F90
https://github.com/ElmerCSC/elmerfem/tr ... moElectric