Debra, of course you can use the photos of your tiels you once owned. The photos are yours that you took. That is the main thing I stress that the photos either belong to the entrant or you have permission to use them here.
I remember Dianne winning the first competition with a photo of a butterfly. I don't think she owned that winged creature. LOL Just being silly here. Yes, please do use your fabies you raised and found wonderful homes for. What better way to honor their loving memory you still have of them and the time you shared with the darlings.