I'm assuming you mean that they leak only when the sea cock is open? If the sea cock itself is leaking, then they require disassembly and resurfacing for a tight fit. Which is why people use bronze ball valves now. If the sea cock itself is leaking AT ALL, then it defeats the purpose of the thing itself. May as well not have them. If they are leaking, and you don't want to haul again, then you had better make sure the rest of that stuff is bomb proof!
And speaking of bronze, don't mix and match materials. As has already been said. Bronze thru hull
? Bronze valve. Bronze valve? Bronze fittings.
Teflon tape is intended for small fittings with small threads. If one wrap won't do it, neither will two or ten. It might not be leaking, but it's not the right product or intended application. If you have so many tape wraps that the threads are essentially full, then you have compromised the strength of the joint.
Use teflon pipe joint compound on the big stuff.
Personally, I don't use plastic fittings below the water
line. Not on thru hull
connections. I'm to clumsy. It's too easy to over tighten them or tromp on them accidentally. And a lot of that stuff seems to fit and tightens up, but the threads are not exactly the same. They are all a little different, And they leak. I suspect this may be the root of your problem. And no amount of any sealant
will fix them. Especially if you ever have to take it apart again, which you should be able to do.
I would close the sea cocks, remove ALL that plastic stuff, and replace it all with bronze fittings and pipe joint compound.