Hi Squirrel and welcome to TP,
Well I'll start by saying well done for attending the AZ meetings - that's a bigger step than you realise and if it is as good as our local meeting will be a great source of help and support to you.
Here on TP there is also a great wealth of support and information available and I have found it invaluable in helping with the stress of dealing with dementia on a daily basis.
The denial is trickier to deal with because basically you just can't force someone into the reality of this - and I should know as I've been battling with my dad for three years now and he's still in a level of denial.
To some extent it's understandable as let's face it this is a horrific thing we're dealing with and for me it sometimes feels like a one way path that there's no way of stepping off or turning around. This disease is as tragic as any other out there and your partner and his family (and you) all need time to process this and grieve.
All you can continue to do at this time is support them, direct them to other areas of support when you can't help them (such as TP or AZ society) and remember to try and put up some bounderies (for want of another word) so that you can shut it off and look after yourself when it starts to become overwhelming.
Try not to feel guilty about doing that as the only way you can continue to support your partner and his family is if you occasionally recharge your batteries and have some down time as it were. Your partner will also need that so do encourage him to look after himself too.