Yes, with most grammar sixth forms this should be okay! If you have any ideas in which ones you would like to go to ask them or contact them and ask for their entry requirements then you will know for sure! Hope this helps
It depends how competitive the sixth form is and what the grade requirements for your course are. If it is a very good sixth form then I expect there will be others with more competitive GCSEs than you but it doesn't mean you won't get in. They'll take other factors into account such as extra curricular s, interview- personality e.t.c.