Hi Robles
When you apply for OH's Spouse visa they should give him a subclass 100 Permanent Residence visa straightaway because (a) your relationship with OH has subsisted for longer than 5 years, plus (b) there is a deoendent child of the relationship.
Because you are an Australian Citizen, you can sponsor your m-i-l once you have been living in Oz again for 3 months, as previously discussed.
Please check the Balance of Family Test to ensure that Nan is abole to meet it:
Aged Parent (Residence) Visa (Subclass 804)
From your description, Nan's son in Melbourne could Sponsor her for a subclass 103 Parent visa immediately but it would be counter-productive to do that. The reason is because Nan cannot apply for a subclass 804 Aged Parent visa unless she is physically in Oz at the time.
DIAC themselves do give out a completely mixed message with regard to onshore visa applications. Ask in any DIAC office in Australia about what to do for Nan and mother in Law and the staff would suggest that you arrange for them both to travel to Oz on 90 day ETAs and simply apply for Aged Parent visas once they arrive. This demonstrates a comlete disregard for both the strict wording of the legislation and the Policy underpinning it. Nonetheless it is what you would be told and it is what your OH's uncle would be told if he went to the local DIAC office in Melbourne to enquire.
It is also a fact that a LOT of applicants for Spouse visas travel to Oz on 90-day ETAs and apply for the onshore Spouse visas when they apply. Everybody knows that they do it deliberately, they seem to think that there is an either/or option about it and DIAC staff do not seem to disagree! There is no difference between the actions of the prospective onshore Spouse and the prospective onshore Parent respectively.
Once could argue that this turning of a blind eye encourages a disregard for the Law that DIAC are supposed to uphold. No Registered Migration Agent would be able to encourage this idea on a public forum. Consult an offshore Agent privately, however, and he is 99% likely to ring from the same hymn-sheet as DIAC's own staff.
I'm not a migration agent and I am outside Australia so I am not fettered in what comments I can make about the situation!
Nobody can guarantee that Nan and her daughter would not encounter difficutlies in trying to enter Oz on 90 day ETAs. That is in the lap of the gods. On the other hand, for a loving mother to want to make a short visit to her only child soon after he arrives in Oz to start his own life is perfectly normal. If his 85 year old grandmother also wants a look at the situation, commonsense is for her to travel travel with her daughter. Nothing is more natural.
After arrival in Oz the two ladies consult a Registered Migration Agent in Oz very promptly. He explains that for technical reasons, they have more visa-options that they thought they had at the point of arrival in Oz. As long as the intent to try to remain in Australia indefinitely is not formed until
AFTER arrival in Oz, the legislation contains nothing that prevents two onshore Aged Parent applications from being made.
Do use 90-day ETAs though because they cannot attract Condition 8503 whereas the lsubclass 676 standard tourist visa can and frequently does.
Best wishes
Gill