Can I type/help write a witness affidavit for immigration when my parents do not write in english well enough...I type faster

Yes, you can.

I sometimes put a sentence at the end of the affidavit: "All the above statements were read back to me word for word in my native ____________ language. " You don't need to say that you typed it. Most affidavits are typed. If this is for your immigration case, are you receiving any legal help? If yes to the first and no to the second, you might consider at least getting a consulation in person or by phone to make sure you are doing the right things. Immigration law is rarely straightforward and reasonable. Good luck.

Yes. You may assist your parents in the preparation of affidavits, declarations, and supporting documents.

I agree with my colleagues. I don't see any issue with you helping your parents out.

Please do. Help the parents. It is indeed a good deed and completely permissible as long as you explain to the verbatim what the affidavit says, in their native language.