I'm afraid more context is need to answer this question.
It's not a sentence for starters. There is no verb.
I also note that there are quotation marks around it. If they are there to show an actual quotation, then your punctuation is probably okay, because you cannot reword your sentence without altering the quotation.
I am not keen on the comma. There is no real justification for it other than causing a pause. A dash is a much safer option.
The credit for making Franz Kafka internationally famous as a writer belongs to his friend, novelist Max Brod, who despite Kafka’s dying wishes, edited Kafka’s unpublished manuscripts and then had them published.
This was a SAT question. Is the punctuation correct?
I note your propensity to put punctuation marks inside quotation marks. That almost certainly makes you an American. (Here in the UK, we tend to follow logic with regard to punctuation and and quotation marks; whereas, in the US, you tend to put everything inside punctuation marks regardless of logic.) That aside, here are my thoughts on your questions. I wish I had the time to hunt down some references for you, but I'm afraid I do not. Perhaps,I'll revisit your questions over the weekend.
Okay, here we go:
He would have been very happy. No doubt about that, absolutely none at all!
I would punctuate this:
He would have been very happy. There is no doubt about that - absolutely none at all.
However, I note that you said it was an email. Looking at the context offered, I would leave it as it as you had it. Non-sentences (or sentence fragments) are fine in an email of that nature in my opinion.
The credit for making Franz Kafka internationally famous as a writer belongs to his friend, novelist Max Brod, who despite Kafka’s dying wishes, edited Kafka’s unpublished manuscripts and then had them published.
This would raise very few eyebrows amongst grammarians. Being very strict, I would have liked another comma before 'despite'. This is because 'despite Kafka's dying wishes'is a parenthesis. The writer could equally have used two dashes, two brackets or two commas. In your example, the writer has only use one comma. The one before 'who' is present for a different reason. I would have written it:
The credit for making Franz Kafka internationally famous as a writer belongs to his friend, novelist Max Brod, who - despite Kafka’s dying wishes - edited Kafka’s unpublished manuscripts and then had them published.
That's my brother Jake.
If you are not addressing Jake, then this sentence is punctuated correctly. Placing a comma before 'Jake' puts 'Jake' in the vocative case. (The case used to address people directly.)
Of course, you could argue that a comma before 'Jake' could also be there to show that 'Jake' is in apposition to 'brother'. That would be an acceptable use of a comma, but it presents the ambiguity with the vocative (as explained).
I think it is irrelevant how many brothers you have.
Answers to questions like these can be found on this website: www.grammar-monster.com
It's completely free.
Do you put a comma before "as"? When the as starts a clause or a phrase that is adverbial in nature (e.g. 'as I said yesterday' or 'as I always do') then you can precede it with a comma. If you start the sentence with such a term, then you should use a comma after it. If you end your sentence with such a term, then you have a choice of whether to use a comma or not.
I hope you can unpick your answers from that little lot.
Regards
GM
PS Don't fret. Your grammar is strong. That is evident from your questions and your hyphen in 'home-schooled'.