what are the admission/ acceptance grades for universities in US (to study law)?

Generally, you need about about a 3.00 for your undergrad. Law schools tend to look most at your LSAT score.

Pointless. You would have to return home after your studies and a U.S. Degree is useless in the UK.

You need a four year Bachelor degree before you can apply to law schools. You will need at least a 3.0 for any Graduate school and for Law you will need to take the LSAT exam. Law school is three years, then you must take the Bar exam to practice law.

You would study US law. You would not get a job in the US as a lawyer. And an US Law degree isn't going to do you much good in the UK.

As you can see on this web site, you will need at least a 3.4

https://lawschooli.com/gpa-medians-law-schools-2015/

Doing law in the US is not much use. Getting a job in the US will not just happen.
US law degrees do not mean anything here in the UK.
Studying in the US is extremely expensive. Their dorms are all shared rooms.
The US education system is very different to that in the UK. Most US universities will not recognise UK A levels. Not only do you have to pay tuition and living you have to pay healthcare insurance. No NHS in the US.
Then you have to get a visa to study there and that may prohibit you working.