I485 Application: First Name and Last name question on the Birth Certificate. ?

Best to indicate BC name and indicate other names under appropriate section.

Yes the application will likely be sent back so it can be mailed to proper address.

Lease agreement, utility bills, bills addressed to both at same address, bank statements, etc. may be used to establish cohabitation.

Best to file by paper and indicate by hand or through options available on form.

You may indicate this with explanation on the appropriate section of form.

This should not impact a subsequent green card filing although it must be disclosed.

Do you have an underlying visa status?

You may not have a travel document number but should include visa number, passport number and I94.

Can I skip my step kids information on my I-485?

No you must include step kids on the I485.

I-751 extension notice

Contact USCIS directly or schedule an infopass appointment to request additional extension.