Difficult friend - Colegiul National Mihail Eminescu (Satu Mare - Roumanie)

Somebody would like to invite six friends we will refer to as number 1, 2, 3, 4, 5, 6. Unfortunately,
some of his/her friends don’t get on well :
— 1 doesn’t get on well with 2
— 2 doesn’t get on well with 1, 5, 6
— 3 doesn’t get on well with 5
— 4 doesn’t get on well with 5
— 5 doesn’t get on well with 2, 3, 4, 6
— 6 doesn’t get on well with 2, 5
What is the minimum number of parties this person should have to see all his/her friends ?
How should he/she proceed to have the maximum number of friends at each party ? (one
friend can be present at several parties).