1. Why use flexi's. They restrict the flow, and are more liable to leaking.
2. Why not:
2a. Turn off hot and cold.
2b. Remove old taps and pipe work down to compression fittings on hot and cold supplies.
2c. Slacken compression fittings on hot and cold supply pipes and rotate to 90 degrees from wall. Re-tighten.
2d. Fit new taps.
2e. Pipe from tap shanks down with 3/4" x 22mm compression tap connector (don't forget 3/4" fiv=bre washer), stub of 22 mm pipe, 22 mm full bore isolation valve, stub of pipe long enough to reach supply pipes.
2f. 90 degree 22 mm compression tee, then short stub of pipe into existing tees on supply pipes. Alternatively, if suitable 22 mm street elbows direct into existing tees, but you would have to solder to new pipes.
3. All the above would in my opinion be better done with soldered joints, but depends on whether you have the equipment and experience.
4. If you must use flexis, you can get 300 mm or 500 mm long hoses with built in isolation valves and push fit connectors onto the supply pipes. But:
4a. You need to get a suitable length which will fit onto the supply pipes without tight bends or kinks.
4b. You will need a stub of pipe from the (existing?) tees to connect to. You might be able to get away with using STRAIGHT parts of the existing pipes.
You may find you need to remove the overflow fitting from the bath to get at the left hand (hot?) tap, as otherwise access is quite restricted.