In general, most plans do not allow any form of payment to be changed after the commencement date. Very likely, a joint and survivor benefit cannot be changed. Therefore, the choice of beneficiary has already been made; you both choose the other spouse. Important: this selection of spouse as beneficiary does not mean, "whoever is my spouse at my date of death", but instead it means "whoever is my spouse at the time my payments begin", so that subsequent divorce is not relevant. Usually, so you should verify.
You state in original post, "...the beneficiary was to be revoked...". Since each person's benefit is in pay status, any "revocation" would be an impermissible change under the plan. The divorce decree has no authority to alter the plan. Also, your children and/or trust will not be relevant, since no beneficiary change is permitted. Also, it is unlikely a QDRO could change anything because a QDRO has no authority to require the plan to do something outside of existing plan provisions.
As far as I can tell from your description, there is nothing to be done. Whichever of you (exes) outlives the other will receive the relevant survivor benefit from the deceased's benefit form, and no one else will get anything.
A few plans might allow some type of change, but it is extremely rare; you should verify within the paperwork you received at the time of your election. For what it's worth, in my 40+ years as a pension actuary, I saw exactly zero plans that permitted a change of joint and survivor form or beneficiary after the payment commencement date.