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No. There are provisions for individual participants to roll distributions they receive from a 403(b) plan to a 401(k) plan. However, there is no legal basis for a merger of plans, or any kind of transfers between 403(b) and 401(a) plans other than rollovers.
What is the Plan's default beneficiary heirarchy? Typically it is something like spouse, children, surviving parents in equal shares, estate. But thsi should tell you who the appropriate bene is under theplan.
"Believing" is nice, but your question is not fully answerable without knowing whether the beneficiary is the father or someone else. In any event, Step 1 is to undo that intra-plan transfer and put the money (plus earnings, but probably not minus losses) in the son's account. There should be no tax-reporting associated with that erroneous transfer to the father's account. Let us know who the beneficiary is and we can help with Step 2.
Yet another argument for a plan provision that allows for allocations pursuant to an "everybody in their own group" formula. You can always allocate comp-to-comp, if you want. And in this case you would not have to dilute the effectiveness of an employer contribution.