You may file as many I864 as your income and household size.

They will be approved but the need is obsolete after GC approval.

No your mother would need to petition for him separately.

This happens in some cases but I would not be concerned.

Yes this should be sufficient for these purposes.

You will likely be issued an RFE and should work with an attorney for guidance.

Yes you may and can request that USCIS holds the I485 in abeyance. Best to work with an experienced attorney for guidance. Good luck!

Depends on the agency renting the housing.

I agree with my colleague. Do a FOIA request to obtain a copy of the I485 approval notice.

Yes you would still be eligible to file for your wife and daughter. Consult with an attorney for guidance.