Brother is attempting to "co-sponsor" ex-girlfriend's mom; email seems suspect and we don't know immigration laws.

Hello Reddit,

So as the title states, my brother is attempting to co-sponsor his ex-girlfriend's mom. He reached out to me the other day saying that the mom needed a sponsor, and he was willing to oblige. After looking over the email, it seems very suspicious, and from what I've read, my brother very well could be on the hook financially for taking care of her financial needs. I've looked up the guy's name in all of the states that the website states they're based out of the U.S., but nothing comes up. Apparently the mom is married and we don't know why she won't have her husband sponsor her. I've removed their names/law firm's name and replaced them with bland titles, but everything else is typed exactly the way the guy reaching out to my brother wrote it.
The email he received says:

" Good morning, Brother, my name is Lawyer, I am contacting  from the law firm of Generic Law Group on behalf of Ex-girlfriend's mom , The reason of  this email is to explain about the SPONSORSHIP process for Mrs. Ex-girlfriend's mom immigration process. Mrs. Ex-girlfriend's mom is undergoing an immigration process to be able to apply for a permanent residence, for this process  immigration is requesting for a sponsor, unfortunately for reasons of her earnings that are low her son who is her petitioner does not apply to be her sponsor and immigration gives her a second option to get a CO SPONSOR  that would be you Mr Brother .
This process does not affect you in ANYTHING -
For this process we will be requesting the following documents from you:

• Copy of your birth certificate
• Copy of your complete taxes for the last 3 years, 2019, 2020 and 2021, including forms W2 and 1040, if you are self-employed, form 1099
• Copy- Last 3 paystubs (most RECENT 3 paystubs)
• Original- Employment Letter- Employment letter should include the following: Name of the company, employment position, wages, and date of employment started. Must be signed by employer

For any questions I remain at your service.

"Generic Law Group, LLC - " "

Again, this seems suspicious, and there was nothing linked about an I-864 for him to fill out, then again, I don't know anything about the process. Any help would be greatly appreciated! Thank you so much!