Visitor visa for grandparents from pakistan

I am british born but my grandparents are pakistani and want to come to the uk for my wedding in july.

I know that I will have to act as their sponsor - but does that mean that they are required to stay with me too?

I live and work in Birmingham ( in rented accomodation - 1 bedroom flat). However, my grandparents will be staying at my parents in Newcastle. My parents are both retired and therefore unable to show that they could financially support my grandparents when they came over.

So what Im asking is
1. Is is acceptable for my grandparents to be living with my parents even though I ( as the sponsor) live elsewhere?
2. As Im currently saving for my wedding, I dont really have much savings. How much savings do I need to show to "financially support" 2 elderly people?

Any help will be much appreciated!