Provided your wastegate actuators are working properly, the reason you can't keep boost down is because the internal wastegates are too small. You can get those things high flowed which will help, or you may need to use an external gate if you intent on keeping those turbos.

Usually a sign of an outflowed wastegate though, is that boost will reach the desired level and then begin to climb with revs. If boost jumps from 0 straight to ~14psi then I'd be looking elsewhere.

Another thing worth noting is that if you have outflowed your wastegates by so much that it is reaching 14psi then I'd say you have some seriously undersized turbos which will be miles out of their efficiency range and therefore creating lots more heat.

I reckon being a M.E should give you the knowledge to build a reliable turbo A-series!