There's no rush for anything here, although I can appreciate that you might like to get it out of the road sooner rather than later. The deadline for the final T1 is April 30, 2021. You're certainly going to want to wait for a few months until the family receives the final T4A(OAS) and T4A(P) for 2020 and collects some records on whatever assets the father owned and what might have been earned up until April 21st.
You do not have to wait until next year. If everything seems to be in order and you have all the details you need, you can "early file" the 2020 tax return using a 2019 T1 return. Assuming the father was getting CPP, then there will be a death benefit of up to $2,500 coming to the estate. That can either be reported on a T3 or divided among the beneficiaries if there are only a few and reported in proportionate amounts on their own 2020 tax returns next spring. Hopefully you've seen the various discussions taking place on this community forum about the choice between reporting this on a T3 or individually by the beneficiaries. Of course, if there are numerous other sources of income to the estate then you'd want to wait until all those are settled and then report everything on a T3. That return is due within 3 months of the trust's yearend.
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