It seems like even after over two years here your heart is still in the UK James, something you have in common with a lot of migrants to Oz. I imagine if the economic situation was better in the uk and your son was keen youd be back home in a flash. I wouldn't beat yourself up about it though, settling here is a hard thing to do. You are obviously someone who speaks from the heart and you feel comfortable expressing feelings and emotions, you probably havent found these personality traits in many aussie blokes.
It can be pretty hard when you first meet aussies particularly blokes, to crack the stereotypical robust exterior but it can be done you just need to adapt, that doesn't mean pandering to archaic opinion if its there, it just means basically 'toughening up' a bit. I have worked with a couple of true blue, fair dinkum, aussies in the trades every day for over a year now and they are now very good friends, despite the fact that I think some of thier opinions belong in the 18th century and i know they think at times i talk rubbish (theyd use a different description) particularly about the uk. Along with my wife we have got to know thier families and circle of friends who we can now call our friends. Its not the same as when we catch up with people in the uk who we have known for 20 years or more but considering two years ago none of us knew eachother its great.
Funnily enough as great as it is its made us really appreciate our friends and family back home and those long standing ties that can only develop over years of shared experiences, and among other things that has brought us to the conclusion that at some point, we will be heading back to the uk, but not for a while.
I think if you can foster a few Aussie friendships here James things will be easier, its always better to feel you are part of a place which is hard if you don't really get it.
You mention you find the Aussie directness hard to deal with, have you tried just being the same? I find it only really leads to conflict if you take yourself too seriously, a trait which most aussies will pounce on straight away. Its helps to have a thick skin here but also be prepared to have a joke at your own expense, you will be surprised how quickly defences come down.
And don't be worried about being a whinging pom from time to time, the aussies whinge constantly! If you are passionate about something from your homeland talk about it, the aussies aren't shy to talk about how great oz is. Basically don't feel you have to be someone else to fit in, you aren't going to get on with everyone but the friends i have made here know where my loyalty lies and wouldn't expect any different, in the same way that i wouldn't expect an aussie living in the uk to suddenly start wearing an English Rose.
As far as the church goes I'd try another, I don't know much about religous groups but I would imagine its like any club, if the people aren't right move on. We have also made a lot of friends, both Aussie and non Aussie through a sports group, they have social events and we catch up idependently as well, some people also take kids along. We had never joined a sports group before we got here but its been great.
Like I said at the start it seems like your heart is set on a return to the UK but now is about the worst time to do it. Try easing into to some friendships and while you bide your time things will become easier. As far as the family health issues at home, this is something all expats have to deal with at some point and only you can decide whats best but talking it over with friends here will be a big help.