Answers:
Yes, as long as they are back to back
There's more than one, two or even five things that could have gone wrong. the cause of your low hot water pressure could be debris and sediment in taps, water leaks, blocked filters or a faulty tempering valve.
Flexi hose can have a limited life and is often quite small bore, whereas 15mm is much better and will provide a noticably greater flow. just a single 90 degree joint may be needed and if you select a top tier brand such as hep2o or speedfit they are reliable and have good warranty periods.