The OP didn't mention whether the 2 new brass frame .44 Piettas are Remingtons, Colts or a mix.
If one is a Remington having a top strap over the cylinder, then it may be able to handle an extra 5 grains of powder (up to 25 grains) depending on the powder. 777 is probably one of the powders that should be kept under 20 grains and if Pyrodex P then maybe only load 22 grains. These powders are more potent than Goex and American Pioneer powder.
Or if the OP would rather shoot stout loads, he could sell them and buy a steel frame revolver. But once they've been fired they will be worth less.
No one really knows how long a brass frame revolver can last. Probably at least 5000 rounds if they're Remingtons, and maybe even double or triple that number if pampered. Remingtons can sometimes be fixed back up by installing bushings or they can always be sold for parts.