Are your varieties determinate or indeterminate? You can force determinate varieties to set fruit by topping. This is a practice used in higher latitudes, when you’re trying to get fruit inside a short summer season. Indeterminate varieties take longer to fruit but will keep going until first frost. This is a vine type, so it needs a trellis, as opposed to cages used for determinate varieties.
If you aren’t sure which one you have, a google search on the variety name should tell you.
- Tomatoes should be able to grow new flowers out of suckers. As far as I know, old branches won't grow any new flowers.
- I've had cuttings of suckers root in less than a week. I have better luck with younger growth. You also will want to cut off most of the leaves from a cutting, otherwise it'll be spending all its energy keeping existing growth alive rather than growing new roots. I've had other parts of the tomato plant root, but suckers tend to work the best.
Most likely what will happen after topping is the plant will fork into two large branches at the closest node to where you topped the plant. The plant will still try to grow mostly upwards with these two branches, and they'll probably grow their own suckers. This is assuming your plant is indeterminate.
I usually don't have much luck with topping off a plant, then trying to root the cutting from that. I'm sure its possible but I usually just throw it in the compost bin.