It's a valid point. If your mother were to stumble into them, she could do herself some damage. If you *really* want taps there, maybe you could box them in, with a hinged lid for when you need to use them.
I would support the ply as much a possible - probably with 4 pieces of timber - one immediately either side of the pipes and another at each outer edge of the ply. If you do that, 3 x 3's should be ok rather than
3 x 6.
Part of the problem is that if your expectation is that it will leak, it probably *will*! You need to show it who's the boss! As others have said, push-fit is easy to work with and fairly idiot proof. And if you do keep the taps, and decide to re-pipe them, it's worth considering braided flexible pipes for the last bit up to the taps. You can get those with a tap connector one end and a push-fit connector the other end - some with built-in service valves. Assuming they're 3/4" taps (which bath taps usually are) the push fit is likely to be for 22mm pipe. The only possible problem would be if the existing pipes are 3/4" imperial rather than 22mm metric - which would depend on when they were installed. If that were the case, you'd be better off with a compression fitting at the other end. Imperial 3/4" is only slightly smaller than
22mm, and you can use 22mm compression fitting with special olives. The difference - although only a gnats - is too much for push-fit to seal reliably.