I agree with Geo_au. The ATO will send you an Invoice after you...

I agree with Geo_au. The ATO will send you an Invoice after you have lodged your return and they have calculated your liability. The timing normally buys you 1-2 months after May. If you are going through an Accountant it would be advisable to get on the front foot and let them know your situation when you lodge your return(s).
The other important consideration is to look at splitting the CG with your wife/partner. I don't know your situation but if your wife is full time home duties or only works P/T you can split the CG with her. I trust your wife has a Tax File number.

Your Accountant will be best placed to advise but IMO I would not recommending selling your shares at this time. You will be able to work out a monthly payment plan with the ATO which will hopefully be manageable and when we resume trading you can decide then when best to sell.
Good luck with whatever you decide.