The sentences (3) and (4) mean same thing. In an elliptical sentence (#3), the final word can be dropped. To me, the sentence (1) has certain ambiguities. As a conjunction, "as well as" generally means 'not only..but also’,’ besides', 'in addition'...etc. So, there is a chance that one might interpret the first sentence as 'He plays not only tennis but also his father'.
Oh, I see the ambiguity in the sentence (1) now. I can say, for example, "He plays tennis as well as football". And it is correct then, isn't it? But when I write "father" as the final word, it really may imply "He plays his father"! :-D
MrPedantic, is it correct to use "does" in the end of the sentense 1b, "He plays tennis, as his father does"? Or I must place it ONLY where you did?