When you're dealing with sibling friction over money, these guidelines may help steer you toward a satisfying resolution for the parties involved:
1. Assess the level of good will. If relationships are impaired but still workable, it may be wise to have a mediator or a trained therapy professional join you to help family members negotiate about the situation at hand. This will free you to exercise your financial and practical skills without becoming tangled in emotional conflict. If hurt, anger, and recrimination have built up to toxic levels, I'd recommend that all parties first seek help from a therapist or counselor to sort out and lighten their emotional baggage.
2. Try to get the siblings' parents on board. In general, I advise parents not to make decisions that their kids will have to try to interpret after their deaths. This can lead to acrimony and escalating conflict. It's far better for a parent to divide assets in advance, fairly and sensibly, having communicated to their spouse and children not only what they are doing but what they hope to achieve.
When sibling money issues are rooted in parental decisions, ask Dad and Mom to explain their wishes and desires. If there are any reasons not to treat all sibs equally, make sure everyone understands them. Discuss what the other sib(s) need or want to feel well taken care of.