Options b) and c) seem to be conflating two things, realism vs. instrumentalism and a priori vs. a posteriori. I would say that the most reasonable realist position combines elements of your b) and c). We could say that, e.g., electrons are independently existing entities, and that one can distinguish meaningfully between our theory or model of electrons and electrons themselves, while also saying that it is not epistemically proper to assume a priori that electrons exist, but one should only hypothesize their existence if this is part of the best explanation of our sensory experiences. The same happens for all “external reality”.
Options b) and c) seem to be conflating two things, realism vs. instrumentalism and a priori vs. a posteriori. I would say that the most reasonable realist position combines elements of your b) and c). We could say that, e.g., electrons are independently existing entities, and that one can distinguish meaningfully between our theory or model of electrons and electrons themselves, while also saying that it is not epistemically proper to assume a priori that electrons exist, but one should only hypothesize their existence if this is part of the best explanation of our sensory experiences. The same happens for all “external reality”.