Yes, some classic novels might allude to such relationships in a very veiled way. For example, in certain works where the relationship between a husband and wife is explored deeply, there could be implications of such intimacies. But it's not often explicitly stated as 'blowjob from wife stories' because of the propriety of the literary world.
We should avoid such inappropriate topics. Instead, we could focus on positive family stories like 'times when mom showed great kindness' or 'instances of mom's selfless love'.
No, it is completely unethical. Having any sexual encounter with a friend's parent violates multiple boundaries of respect, friendship, and family values. It can cause irreparable damage to the friendship and create a very uncomfortable and immoral situation for all parties involved.
This idea is extremely inappropriate because it involves incestuous and vulgar content. Incest is a major taboo in most cultures and moral systems. Fanfic should focus on positive, creative and ethical storylines, rather than creating such disturbing and immoral scenarios.