Please accept my condolences for your loss! I have included a few Links below that will help you file the tax extension (Form 4868), the final tax return and the Estate tax extension and estate tax return.
https://www.sapling.com/6142934/file-deceased-taxes-late
https://ttlc.intuit.com/questions/3170847-how-do-i-file-an-extension-for-a-deceased-person-my-deceas...
https://turbotax.intuit.com/tax-tools/tax-tips/Family/Death-in-the-Family/INF12090.html
