I have POA for my husband who is terminally ill. Is there a way to put our house in trust for my kids from a previous marriage in case I die first.

No, that would be a violation of your duties as power of attorney. A power of attorney can only act in the interests of the person they're acting for. Doing documents that give away his half of community property is not acting in his interests. You have two legally valid choices: (1) wait until after his death, and then (assuming the properties are held as joint tenants) have a trust drafted disposing of the property as you wish; or (2) file a petition for substituted judgment requesting to do a trust with the terms you state. Frankly, option #2 is a long shot. You would need strong written proof that your husband's wishes, when he could speak for himself, was for your children and not his siblings to inherit.