US Immigration from England

Hi everyone

I have a couple questions about the affidavit of support...

Due to covid-19 my income is way below the required amount. I only worked a few weeks in 2020 (i'm immunocompromised so I locked myself down early) My total 2020 income is less than $2,500 and I only have around $4,000 left in savings + $3,000 in stocks. I'll be returning to work full time after I receive my second vaccine dose, but I don't think I'll have enough paystubs by his interview date to put me over the minimum on my own.

My mother is willing to co-sponsor and makes around 70k per year and my fiance has around 40k in savings. (I've heard that he can self sponsor in London??) So I'm hoping between the 3 of us it will be enough.

Anyway, my question is; which forms do I need to fill out for them? I've filled out my i-134 and have started the i-864, but do I need to fill out an additional i-864 for each of them? Or do I just fill out my i-864 and then the i-864a for my mother & fiance? And for my fiance, what proof will they accept for his savings? Does it need to be a letter from his bank stating the balance or will a bank statement be enough?

Sorry for all the questions and thank you in advance for the help!