There is no prohibition against bringing babies to USCIS interviews.

If you are eligible, you may submit the N-400 even if the I-751 is still pending.

One cannot petition for grandchildren. You may petition for your son and he maybe eventually arrive as a LPR, but it will likely be too late for...

You may tell the officer about these changes during the interview.

You should not travel internationally. The immigration court has jurisdiction over the I-485 application, assuming that the I-130 is approved.

If you are eligible to adjust status, you may submit the appropriate package to USCIS, but you will not be refunded the NVC fees.

Assuming that the letter is received by the correct office, USCIS usually sends a letter acknowledging the withdrawal shortly afterward.

You should be able to re-enter as a LPR.

You may need to do an Infopass with your local USCIS office to track where your case is. If USCIS still has not acted on your case, consult with...

Depends on the particular immigration judge. Some make decisions within 30 days; others will make the decision at the next scheduled court...