Filing ROC i-751 online advice

[Skye841 1]

Hi, sorry if this is repeated or seems silly to ask. I want to file the i751 online. The uscis link to how to file online tips state you can sign by electronic signature. Now when i went to start the form it says you can only file by pdf upload (see attached). So has anyone filed online and what does this mean before i go further? Do i now print the form and fill in and sign physically and upload it back into uscis then attach all my evidences? Or does the form and all evidence need to be in one big pdf file to upload to uscis? Because that seems way too large for a file to do it that way? 
Also part 5: list all children. Is this if i have any biological children? Because i dont, but US citizen husband has grown children from a previous marriage, no longer do they have a relationship so we dont have addresses either. So are they supposed to be listed or i can just put n/a because they have nothing to do with my case or us. 
appreciate any advice thanks

[Edward and Jaycel 2,538]

The first thing it is going to ask you to upload is the I-751 Form which you should fill out, print sign and scan into a PDF to do this upload step. Upload the signed form (signed by you and your spouse). Then you will upload evidence separately