debt settlement.. all at once or one at the time?

I have about 18 different CC from flavor of creditors: HSBC, BoA, Citi, Chase, AMEX ast due 90 days now, I slowly start talking to them get agreement in writing bacause before I pay anyone anything I need to be sure I have all on board for settlement otherwise I will pay nothing and file for BK ch.13 so here is my question obviously they are telling me here is our agreement and is due by ... if agreement is not kept they have no obligation to extend same one in the future which I'm sure is just talk way they ant me to pay right away but if they want their money they will re-do and re-fax same agreement next month with slightly higher numbers because of late fees and interest... in any case i.e. I have 4 amex cards now in hands of CA, amex was quick with this they turn over to CA within first 60 days so should I get 4 greements for each of this card and pay at once to avoid situation where I pay 1 card and then they will tell me I did not fulfill our agreement and now there is no agreement for rest cards and they will demend full payments or do all at once? I would prefer do 1 smalest card just to see if they words about closing my account are worth anything and risk loosing couple hundreds of $ or pay all 4 amex CC and let them take over 10k in settlement and still try to get remaining balance or re sell my remianing balance.

any advice?

TIA