So if we stump up the cash for the Settlement Visa for my wife, can the UKM then be applied for once we're in the UK?
I believe so.
The spousal visa rules are quite strict though, so you would need to ensure you meet all the requirements when you apply for it - financial documents, evidence of your accommodation in the UK, relationship evidence etc.
Also, it is taking a few weeks for the settlement visas to be processed at the moment - if you pay an extra $300 on top of the £826 visa fee for Settlement Priority Processing, it's taking about a month once the application is mailed to NYC (after applying online and attending a biometrics appointment) , or it's taking 2-3 months if you don't pay the extra for priority processing.
Also, can my wife (traveling on the Settlement Visa) and kids (traveling on their new UK passports), travel on One way tickets to the UK?
Yes, they can, although often it is actually cheaper to purchase a round trip ticket and then just not use the return portion (or save it to use for a trip back to the US later).
I stumbled across a 'Returning Resident' entry. Since my wife lived there from age 11-24, got married to a UK citizen in the UK and has a mother who is a UK citizen, do you think that would be an avenue we can pursue? It'd be cheaper than a Settlement Visa for sure, I believe around $446 as opposed to $1363.
In the 6 years I've been a member of this forum, I have never seen a Returning Resident visa application be approved. All of them have been refused... even when the applicant grew up in the UK and still has all of their immediate family members living in the UK.
In the last 4 years, 12,724 spousal settlement visas have been issued in the US... but in comparison, if you look at the number of 'Other' (not spousal or child) settlement visas issued in the last 4 years, the total is 6 (I'm assuming 'Other' includes elderly dependent relatives and returning resident visas, because I can't find a separate category for returning resident visas).
Personally, I wouldn't even attempt to apply for it - she's much more likely to be issued with a spousal visa than a returning resident visa.
Also, she must meet specific requirements to qualify for a returning resident visa:
1) She must have held permanent residence status in the UK before she left
2) She must have left the UK within the last 2 years
3) She must be returning to live in the UK permanently
4) She must not have claimed any public funds while in the UK
Plus, if she has a mother who is a UK citizen, and uses it to try to get the returning resident visa, then UKBA might question why she is applying for a visa when she can just register as a UK citizen instead, which would be cheaper and easier for her to do.
Honestly, in terms of immigration, the most hassle-free and cheapest option would probably be to do the UKM application and get her a UK passport.
Is there any way you can go to the UK ahead of her (and the kids?) to start your job, and then they can join you when they get their passports?
You haven't got all that long until you start your new job (6.5 weeks) and there's no guarantee that you will have your kids passports (which take at least 6 weeks), or either your wife's visa (1-3 months for processing) or UK citizenship (2-6 months for processing) by then either... especially as you won't be able to book flights for the kids without their UK passport details, and if you're applying for a visa, your wife should not book any travel until she has her visa in her hands and has checked it for errors, which probably won't be until mid-late April at the earliest.