Yes, your Thanksgiving may be tinged with sadness this year and that is to be expected, for you are still grieving over the loss of your father and the decline in your mother's health. Within the last few months, I have lost one of my sisters and also a sister-in-law, and I have been reminded again that grief is something that fades only very slowly.
But your Thanksgiving should only be "tinged" with sadness, because the main emphasis should be on thanksgiving and joy. And it can be! Take time to remember the good times you had together in the past, and pause to thank God for them. Thank Him too for all that your parents meant to you over the years. And thank God also for the family ties that keep you coming together each year.
In addition, thank God for all His good gifts to you during the past year. All too often we focus on the bad things and forget the good things; God blesses us in ways we easily overlook. The Bible says, "Praise the Lord, O my soul, and forget not all his benefits" (Psalm 103:2).
Most of all, thank God for the gift of His Son, the Lord Jesus Christ, who gave His life so we could live in His presence forever. Make Christ the center of your celebration this year, and it will be a true Thanksgiving. The Bible says, "Thanks be to God for his indescribable gift!" (2 Corinthians 9:15).