How do I reply to a mail with in-line comments on iOS?
IOS support also what you need:


from upper right icons of the received mail, press the curved to left arrow to generate a replay;
press return on the line where you need to write an answer to create an empty new row;
on your keyboard, upper right, touch/press the letters "B" and "I" to generate bold and italics. Please note these letters become color blue;
type your answer. It will be written in bold italics;
send as usual!