1) TURN RESPONSIBILITY BACK TO THEM
One of the first thing many effective managers ask when employees approach them with a problem, concern, obstacle, decision, or issue is to ask, "What have you thought of or done so far?" This helps the "helpless" person learn not to run to Daddy or Mommy at the first sign of a problem. Part of coaching a person is to help turn them back to their own resources instead of training them to become overly dependent upon some authority figure. So we do suggest that you ask the whiners this question, so that they see that your time is also valuable so that if you choose (key word!) to continue to support them emotionally, they must do some homework of advanced thinking, brainstorming, and action steps before coming to simply dump on you. Otherwise, you are like a parent being overly permissive with a screaming child in a grocery store who does not take charge–– you are letting your own resentment build. In the process of asking what they plan to do or have done, perhaps you'll enjoy a side benefit of the reputation getting around that you are willing to help but only if others take ownership for thought and action.

2) ASK WHAT THEY EXPECT OF YOU
Many "advice specialists" like you assume whiners want your advice when they really may want to just vent. Before making suggestions, besides asking the above question, check out exactly "How can I be helpful to you two? ... What is it that you need or are hoping to achieve by talking to me?" At least it forces the "shoppers" to figure out if they want emotional support, ideas for fixing the other, role-playing help to practice clearly and fairly expressing their frustration and request, assistance in taking the complaint higher, etc. Then you are in a better position to decide if you can or want to provide what's requested. Often times, people can be like bottomless pits asking for advice, but every suggestion is met with a "yeh, but" or "that won't work because..." Do they REALLY seek to solve the problem or just whine? Don't buy in. Instead, get clarity on their true goals.

3) DON'T GET SUCKED INTO GUILT
Is it part of your job plan to spend endless time with their complaint? Was your mother a travel agent for guilt trips? If not, take care of your needs, be straight with them and let them learn to solve their own problems. If you DO feel guilty, recognize this means you are having a trip laid on you. Often times, underneath guilt there is resentment (like you're feeling and they are feeling) so before you feel guilt or resentment, prevent these emotions by taking care of your own needs.

4) DON'T YOU REPEAT THEIR BEHAVIOR.
Frankly, if humor does not work, I'd suggest more direct though not mean communication. Since they are not being clear enough in communicating in descriptive, non-evaluative ways how the other person's behavior is negatively impacting them and the team with a request for some sort of agreement about alternative behaviors, they need to provide behavioral feedback to the abusive, dominating co-worker. While your two "children" (you are adopting the parenting role, you know!) are not "meanies," it's time after some coaching and the above tactics, to do with them EXACTLY what they need to be doing with the upsetting co-worker–– share your concerns. Explain that while you want to be helpful, you have limited time given your workload, explain the impact, and even share your feelings how it affects you when they refuse to implement any of your suggestions and just allow the situation to continue. I strongly recommend your reading and then giving them the excellent book on such interpersonal assertiveness, PEOPLE SKILLS: How to Assert Yourself, Listen to Others, and Resolve Others, by Robert Bolton (Simon and Schuster, 1979). It's older but still wiser of books on how to express yourself in such difficult conversations.

5. POLITICS OF POWER
It does not seem that these two have power, but if the coworker is a peer, two years of seniority should not necessarily make him dangerous to their political stock, especially if they confront the situation professionally and calmly. Perhaps you're leaving out an important detail, but at face value your situation and their just requires the Power of Interpersonal Communication, not position power of power politics at work.