My partner of many years as well as myself both lost our spouses. We chose not to marry. His kids absolutely hate me. He realized soon that his kids would not care for him but would place him into care. Their hatred for me was so obvious that several events happened where they mistreated me in front of him. He asked me if I would take on the Trust and totally take over caring for him including his finances. I did not realize the amount of work I was taking on. I have been able to organize everything and have actually made him money by seeing the charges that he incurred using his credit card to buy things that people were talking him into. His kids have not been to see him now for 4 years. They never call and have made it very clear, it is me or them. I realize that what I am doing is best for him. I am an honest person and could not live with myself if I mis-used this trust. When my partner passes, I am to be allowed to live in his home as long as I wish and to sell it on my timeline. I am going to inherit two very small savings accounts. I will be responsible for making sure the kids get their portion of the house. My portion is greater to pay me for my care given him. Can anyone think of something I might have trouble with when the time comes? I have the medical Power, banking and money decisions, I am the trustee should he pass. What obligation do I have to his kids? I have yet to send them a copy of the trust as I don't want to start problems before necessary. I asked my partner about sending them the trust and he agrees that it would only make things harder for me now.
Also check into common law marriage rules for Oregon. You may have more rights than you think.
I think you're wise to be concerned, given the nature of the relationship between your SO and the children. If I were you, I'd document everything you do, especially financial issues, to cover yourself in the event undue influence charges are raised after his death.
There is another alternative, if provided for in the Trust. If your SO named a successor trustee in the event you were unable or unwilling to serve, you could ask that trustee to assume the responsibilities. That would take you out of the firing line.
I don't think that YOU have an obligation to his children, but maybe he does. If he is coherent, he has the right to leave his estate to anyone he pleases, but they may not see it that way. Assuming of course that there is an estate to leave. Depending on his illness, and your abilities to care for him, he may need to be place in skilled care at some point. That will eat up money fast.
I believe you have what is called a life estate in the home. Be sure that is in writing and properly executed.