Hmmm, PT99 ... with the adjustable rear sight.
The older style of magazines with the heel release will interchange.
Present day magazine release is definately NOT interchangeable. The mag catch is in a slightly different place. So....
You can get the magazines to fit, but a littlle work is needed to enlarge the magazine notch.
Taurus magazines will not fit the Beretta correctly, but will fit, as you cannot add metal to the mag notch, thus it will be a sloppy/floppy fit. My concern would be how reliably the follower would push the slidestop up with the sloppy fit.
Most parts will not intechange. Definately not the grips & grip screws, hammer, trigger lanyard and the magagazine catch.
The parts that WILL, that I know for sure are the barrel, guiderod and recoil spring, locking block, hammer spring and slide catch. However, with the locking block ... I've run into issues where it had to be fit, it would not just drop in.
On a side note, I prefer the safety release on the frame like the older style Berettas many moons ago rather than on the slide as on present day Berettas.