Family visitor for minor niece accompanied by grandparents

Would like some advice.

I intend to bring my parents from India to the UK for a couple of months. They currently look after my brother's minor daughter ( around 1.5 yrs old) back home. Currently I am thinking my parents can get my niece with them (my brother and sister in-law will give a no objection letter or whatever is required). We (me, wife and 10month old son) live in a 2 bed flat at present.

1. Wondering whether my niece will get a visa ?
2. Hope 2 bed flat is ok legally for 2 more adults and a kid..

Thanks!