I’d say the World of social media plays a role. Teenagers tend to be introverted when face to face with people now days, they prefer to text and do Instagram etc instead of real social interaction. All you can do is keep encouraging them and have a chat to see if there is something worrying them about being out and about and socialising.

I’m surprised they don’t want to go as they have each other for company. I was very anti social as a teenager too. It’s an awkward age, my boobs grew, I changed shape and I developed acne. All of which contributed to me nit wanting to be very social

I’d ask them why they don’t want to socialise and if it’s just that they don’t want to, then I wouldn’t worry. I wasn’t a social butterfly as a teenager and only started going out socially once I left school.

Have a discussion about family togetherness and going out together and supporting each other. Start off small, maybe one outing a month, fortnight or week to start getting used to going out and being more social.

Is there a reason they’re being anti social? I know when I was a teen, I didn’t like going out when I had zits on my face or when I had my period. They both made me a bit socially retarded for a while

Don’t force them, talk to them, ask them what they are interested in and even if you dont like it or understand encourage it (as long as its not dangerous).
give them freedom to discover what they like without making it seem like a chore to do it. bring home info about things you think they might like but don’t put pressure on it. they may have a very good reason for not wanting to do something maybe find out the reasons why and you can help them find something to suit them.

You haven’t stated how old your teenagers are. Are they worried about the attention of some boys they know who will be attending.
Unfortunately some reckon they have the right to be “intimate” with girls they spend time with. Not all teenage girls have that inclination. Have you asked why they don’t want to attend the events. Maybe they will talk to somebody else they have confidence in but don’t feel comfortable talking to you about it. It is possible they have been bullied or asked for sex by boys at school. I was shocked to find that it happened to a 7 year old girl I know by a classmate. Fortunately she said “no” but was very upset and confused because she knew it wasn’t right at her age and told her Mum when they got home from school. When the school was advised the class teacher was shocked.