No, form E is a long, 30 page form which the Court will order you both to file to set out your respective financial positions.
You don't do that together, and mediators don't help with it.
Form A is the form you need if (as I think is probably the case) mediation has failed, and you need to trigger the court process. A mediator will need to sign one page of that form, so that the court knows you have tried mediation, it has failed, and therefore you can go ahead with the court process.
Neither have anything to do with child arrangements. If you can't agree those, you need the mediator to sign the relevant page of a C100 so you can start court proceedings about the kids.
Alternatively, if you have in fact got a financial agreement, the mediator needs to prepare a memorandum of understanding and an open financial statement, and you need to tae those to a family solicitor who will advise you on the merits, and turn them into a consent application for the Court to consider.
Once the financial order is made and the divorce is final, he can be made to go.