I have similar situations as yours. Did you file your 1st I485 for all of you? We did.
But on if filing for 2nd I485, it seems no positive signs from both side attorneys. But Xiaobaitu explain looks like reasonable as well (no detailed deion from USCIS regulates not allowing to file 2nd 485).
So my understanding is if 2nd primary applicant files his/her I485 only, it might be a good pretective way if there are some problems in first I485.
Please let me know what you think
Thanks.