Neither of these are portmanteaux. To form a new word, a portmanteaux has to use parts of at least two words, more than their initial letters but less than the complete words (although it can use one of the words completely, but not all of them). If you can imagine a scale (with "0' on the left and "10" on the right), portmanteaux are in the middle range, abbreviations are on the far left and compound words on the far right.
With your examples, you would have to have something like "youbanfessional" or "duacomenoids" for them to be portmanteaux. Both "yuppie" and "DINK" are examples of initialisms. DINK is an initialism that is a strict acronym- it is made from the first letters of each word and is pronounced as a new word.
Because most people don't know of any other names with which to describe it, "yuppie" is sometimes referred to as an acronym or an abbreviation. It is neither since: 1) it is not strictly formed from the first letters of it's forming words although it is pronounced like an acronym, and 2) it is not an abbreviated form of a full word. It isn't a portmanteau because we know its forming words and it is not formed from parts of them. The word "yuppie" is a simple initialism.
I hope this helps.