Do I have to join in to the other passports queue in the UK border control with my Australian passport and residence permit while I am with my British passport holder wife and children? Is there any other way to avoid filling a landing card beside enrolling as 'Registered Traveller'?
You will have to fill out a landing card each and every time unless you are a registered traveller. It's the law and there is no way to circumvent this requirement.
Your other question is more interesting... You are directed to the 'other passports' queue because you do not have a British (or EU) passport and you want to join the accelerated queue for British passport holders. There is no set policy on this, but there is an overarching policy that immigration procedures should avoid separating families -- it's something they are reluctant to do.
So under that policy you can join your wife in the British passport queue and clear controls such that your family is not required to be separated.
There are exceptions to the policy...
- the queue are long and the IO's are very busy. In this case they may ask you to wait by the desk until the queue subsides.
- the IO is a dim witted jerk on a power trip. In this case your family will have to join the 'other passports' queue.
- it is your first time entering the UK on a long term visa (I mention this for completeness purposes, it doesn't apply to you).
As a general rule, you should proceed to the British queue as a single family unit (as long as there's a Brit in the party)
For your implicit question: there are no special breaks or carve-outs for Aussies, or any other Commonwealth national...
My American wife and I have joined the UK/EU queue may times and had confirmation from several IOs that it is ok to do so. The problem is that many UK airports employ private security staff to direct people to the right queue. It is usually with these staff that we have had to have an argument!