Forms

Any abagado can handle NIE and Residencia, it's not difficult
I think there is already lots of information scattered through the forum through various posts

You are right, however, charges vary greatly.

I wouldn't pay someone to do your nie as it's a huge ripoff at around 100+ euros just to fill out a single piece of paper (form ex15) and make an appointment with the local police station. Depending on where you move will determine which one you need to go to. Los palacios needs to go to orihuela, but I think quesada can be done in elche or torrevieja. Someone please correct me on that if it's not the case. Out of those two, pick elche as you don't have to make an appointment. You can just show up in the morning and grab a ticket.

All you need for the nie is the ex15 form (there are translations online, but can only submit Spanish version) and a copy of it, two passport photos, a modello 790 form stamped by the bank (it's the payment form and can be picked up at the police station), and your eu passport & copy.

For residencia, you need ex18 and copy, model 790, three passport photos, insurance with hospitalization/pension/job contract/6000euro a person in a Spanish bank, and a copy of your passport. It's also recommended you're signed up to the padron, which is done at the local town hall with your rental/house contract and passport.

However, these requirements seem to change depending on the mood of the officer and which police station you can go to...

The original question was what form do I need to bring, not what forms do I need when I get there. As Casa said they are moving to Quesada shortly then I assume (probably wrongly) that they already have an NIE. If not they won't be able to buy or long term rent a property or open a bank account.
Signing on the register of EU foreigners residing in Spain (residency) can be done after they have got here. Already quite a few threads on how to do that but it has to be done at a National Police station or foreigners' office.
You should not have to prove you have 6000 euro per person in a Spanish bank although some of the guys in suits seem to have made this requirement up. Simply access to sufficient funds and regular income (about equivalent to the Spanish pension) is all that should be required but, again, the guys in suits seem to make things up as they go along.
You can apply for the NIE (if you haven't got one) and residency on the same form at the same time on the EX18. You will need proof of medical cover, either private or state provided if you are pensioner on the S1.
One of the easiest places to do it is the Orihuela Costa town hall where they will give you a list of documents required (in English) although it takes 3 visits (one to make the appointment and get the forms, one to complete the forms and one to collect the NIE and residence card) however they are closed until the 17th of this month.
Abaco solicitors will do it all for you at 70 euro but you will have to turn up at the National Police station in person.

I really wished I had gotten such an answer when I asked about this a few months ago. The person we ended up going with charged us double half way through and it was already way more than the 70 you mentioned! And still haven't gotten residencia...

But jeah, not any documents other than a passport that's needed before arrival. You can open a bank account ana rent without an nie (or at least we did) and sort that all when you get here