I am sorry to hear of your loss.
The legal representative of the deceased must submit a return for the deceased if one is required. They also need to contact the CRA to provide information about the death. The legal representative doesn't have to be one of the children, but if there's no one else to handle this task, then one of them may have to do it.
This FAQ has more information regarding preparing returns for the deceased: https://turbotax.community.intuit.ca/community/product-information/help/can-i-prepare-a-return-with-turbotax-for-someone-who-has-died/00/873466
If you have TurboTax Live Assist & Review, here is how to talk to a Tax Expert: https://turbotax.community.intuit.ca/community/navigating-turbotax/help/i-m-using-turbotax-live-assist-review-how-do-i-talk-to-a-tax-expert/00/873764