As far as proprietorship firm is concerned, following is well settled:
1. S.141 is not applicable.
2. Only prop can be accused.
3. No worker or manager can be accused.
4. The firm cannot be made accused (non maintainable)
Most likely in this case the notice would have been sent in the name of firm and in the name of son (non proprietor), so it cannot be said that the notice is received by actual proprietor, the father. From this angle itself, father cannot be roped in.
A bare reading of S.319 conveys, possibility of adding accused, not changing accused. In this case it will be like changing accused.
Request please provide any case law of HC/SC wherein such matter is dealt?