Is it acceptable if the two opposing attorneys had a verbal agreement?

My sister is the successor trustee of our parent’s family trust. She petitioned the court to approve her accounting and actions as trustee, and for “instructions” as to whether Amendment 1 or Amendment 2 is the valid amendment controlling our trust. All five other beneficiaries and I wanted Amendment 2 to be held valid. The attorney for the trustee offered that she would agree to a joint petition to use Amendment 2 if I gathered all the other beneficiary’s signatures, which I did. The trustee signed her agreement and sent it to my attorney. My attorney paid the filing fees for all the beneficiaries ($2,000+) from my retainer and filed the joint petition to use Amendment 2. The very next day trustee’s attorney presented a proposal/ultimatum from the trustee requiring that I: 1) Exonerate her for her actions even for the period before she became trustee when I allege she embezzled funds from the trust. 2) Agree to her specified monthly “allowance” instead of using the discretionary terms “Health, Education, Maintenance and Support” from our trust. 3) Agree to an amount she claims I have received from the trust. This would have cost me $8,000 due to her miscalculation. If I did not agree she would withdraw her agreement to use Amendment 2. My attorney never even complained to the trustee’s attorney that “Hey we had a deal!” or “Your client already signed under penalty of perjury and it’s been filed with the court”. Instead my attorney started pushing me to agree to the trustee’s horrible terms. He said the trustee would likely be allowed to withdraw from her signed, filed agreement. Can the trustee’s attorney withdraw from his verbal proposal agreement with my attorney? Can the trustee withdraw her agreement after signing it under penalty of perjury? Is the trustee allowed to use her position to her advantage when dealing with the beneficiaries? Should her attorney be paid from our trust when she’s using him to push me around?