I’ve got the exact same problem. I tried to encourage my parents to go, I’m 22, and go almost on a weekly basis.
I think they somehow dont think it ‘matters as much as it used to’, but I have sat with them and discussed how it is a necessity and so forth, but they still go to mass with my Gran and knowingly participate in the Eucharist after what Ive told them.
Its hard, I know, for example, they have major sins to confess, for instance I am aware my father had a vasectomy when I was around 8, and as far as I know he’s never confessed this, because he doesn’t ever go to confession!
Its tough. I also struggle with my younger brother who refused confirmation at school age and is now 20. I attend RCIA as my Priest thinks it will aid me in my discernment to the Priesthood, and I tried to get my brother to come as he keeps saying he will ‘probably get confirmed one day’, I wish he’d either stop giving me an answer he thinks will satisfy me, or just say how he really feels because I think deep down he just doesn’t care.
Anyway all I can do is pray for them all to turn their hearts back to God and the Church. Nothing is impossible to God.