I'm sensing a few bits of confusion here.
No spousal visa path to the US allows your DH to apply for his green card from within the US. The only one that did is a path that has been administratively removed for a few years now. You can now get your DH to the US in a few ways:
- Apply while both in the UK by filing the I-130 directly at the Consulate. This is DCF and nets you a CR-1 visa if you've been married less than two years or an IR-1 visa if married more than two years. Once he enters the country the production for his green card is ordered with no further processing needed.
- Move to the U.S. and file the I-130 with USCIS. This is the same process, done stateside, where it takes longer. It still nets you the IR-1 or CR-1 and the green card once he entered.
It used to be possible to submit the I-129F during the stateside filing process and net a visa called a K-3. However, this path has been more or less closed; it was designed to reunite families faster because it only granted permission to enter the country and additional filing had to be done once the spouse was stateside. Once the processing times for K-3 and CR-1/IR-1s started running neck and neck, USCIS started removing K-3 petitions and converting all petitions to CR-1/IR-1 administratively. So, in a nutshell, K-3 is dead.
Now, as for sponsorship, you must be the primary sponsor for your spouse. A job contract is not enough evidence to sponsor your spouse; you need tax returns and proof of income that will continue in the U.S. That being the case, you are allowed to have a co-sponsor, who must meet 125% of the poverty level for their household size plus the immigrant and provide proof for that. The I-134 is what is needed for a visa like the K-1; for the CR-1/IR-1 route you'll need to look at form I-864 for you and your sponsor and be able to provide the information needed there -- three years of tax returns, bank statements, etc.
