In my experience, all the Yeth an Werin conversation groups I've been to are really welcoming to ANYONE who's interested and wants to come along (including partners/family/friends who don't speak Cornish at all!) — regardless of level of knowledge or confidence or whatever. They're really informal and friendly and fun.
In fact, I know the Porkellis group quite well and they always have a special session for beginners/complete newcomers at 7.30 pm before the more experienced speakers arrive at 8.00. That's the first Thursday of the month, which will be 2 August in your case. I would highly recommend it if you and Patrick are interested — I know they'll be happy to welcome you both. My Kernewek tutor Steve and his wife Dee usually run the beginners' session, so say hello to them for me if you go! Actually, Steve is one of the official contact people for the Yeth an Werin, so do email him at firstname.lastname@example.org if you've got any questions about the evening.
Oll an gwella (all the best) — hope you have a great time!