US Immigration from United Kingdom

My wife (USC) and I (British Citizen) currently live and work in the UK. We have been married and living together for over 3 years here in the UK, but have decided we want to move to the US and have begun looking into the process of applying for and IR-1.

We have a couple of points of concern, as it appears a lot of the case studies and material out there focus on either a) the USC is in the US and the beneficiary is overseas or b) both the USC and beneficiary are in the US already. In our case we are both overseas.

Affidavit of Support

My father-in-law will be a joint sponsor, as obviously neither myself or my wife have current employment or income in the US. Am I correct in thinking that the 'joint' sponsor can take on the entirety of the financial requirements in these circumstances?

We are also planning to live with the in-laws in the short term once we arrive in the US. Will this have any effect on the necessary income requirement? Assuming that he passes all of the financial requirements would this put us at a disadvantage where Public Charge is concerned?

Establishing domicile

As we currently don't live nor have any assets in the US, is there anything else we can do now to help prove that we are 100% planning to move to the US assuming the visa is granted? My wife has already re-opened a bank account there and we have started getting quotes for removals but that's all at this stage.

Thanks all