It sounds as if the estate planning documents that were supposed to provide peace of mind and certainty for family members have only served to create some angst and distrust"”at
least between you and your sister.
A few things to keep in mind: If the durable power of attorney and trust are like most of them, your sister's powers as agent and trustee will not likely take any effect until your parents are either legally incapacitated or deceased, so you probably need not worry abut being booted out of the house anytime soon.
Also, it is at least possible that your sister acted with the best intentions of trying to help your parents get their affairs in order rather than to be devious or squeeze you out of the family business.
But all that won't likely change your understandable feelings of being shut out and left behind.
An interesting and extremely hopeful sign is that your dad, probably unaware of how you felt, expressed a willingness to change the documents. While you are concerned that changing the documents may create more strain between you and your sister, it might actually help in the longrun to divvy up the duties and responsibilities.
One possibility would be to make you and your sister co-agents and co-trustees-although this may not be the wisest approach, since it would mean that you both would have to agree on all actions and decisions. That is a tall order for many siblings"”and may be for the two of you, too.
Another approach would be to share the responsibilities. For example, if your sister is the organized type, it may make sense for her to act as trustee of the trust. And since you are already living with your folks and most likely to know about their daily needs"”it dawns that something about that arrangement may actually be making your sister nervous that she's the one being squeezed out"”it may make sense for your parents to appoint you the agent in their power of attorney.
The most important way to find the best solution: Have a family meeting in which everyone is encouraged to express his or her views and feelings while the others are required to listen and suspend judgment.