How to help two elderly recent raw converts increase jaw strength?

My cats ate kibble and canned food for 15 years and I switched them recently to raw organic grain-free with just small amounts of Wysong Uretic because if Tigger doesn't have it she will absolutely get a UTI. They can eat it, but for example right now it's lamb stew meat on the menu for them and the meat has to be cut into tiny chunks about as big as a pea for Tigger and slightly bigger for Tabitha. The willingness is there-Tabitha will eat huge chunks when it's ground, but their jaw strength is just dismal. Their teeth actually aren't bad and they are generally healthy, strong cats, but you can't expect 15 years of commercial chow not to do some damage. That's something I'll always have to live with I suppose, but I'm trying to help them as best I can. On the bright side, I can already see an amazing difference in them!