Btw, in an earlier posting of yours you said the C64 was your first computer, bought for you by your grandma. I'd try to keep that if I were you, I always regretted getting rid of my first computer.
The C64 and Tandy 1000 should have composite video outputs, that you can plug in directly to many televisions.
The picture of the back of the AT clone is cut off, so I can't see the video port, or if there is a video card at all. These could have anything depending on the installed card.
Also, does the Tandy 1000 have a keyboard with it? Those used a proprietary keyboard.