Not open source, but designed and proven useful for building tools to handle multiple, complex langauges: our DMS Software Reengineering Toolkit.
DMS contains strong parsing machinery (capable of handling difficult languages such as C++) that builds ASTs automatically from just a grammar description, and libraries to support construction of symbol tables, and various kinds of control and data flow analysis.
OP will have to provide grammar and semantical descriptions of his proprietary languages, but I think he is expecting that. If he wants to model flows across the languages, he'll have to organize his flow analyses for the individual languages to be compatible. The fact that DMS uses uniform infrastructure/datastructures to support all these activities even for different langauges will make this easier.
He should not expect a project involving multiple languages to be easy or quick, regardless of the framework he finds. Our intention with DMS was to make this practical.