If you ran through all your savings tomorrow and then died suddenly, who would finance him then? His sisters? I doubt it. They would tell him to grow up, as they have done.
You say he is bad at managing money, as though that is built-in, like left-handedness or blue eyes, but managing money is an acquired skill. It is time he learnt how to do it. None of us are born with an innate ability to spin out our resources so that we are never in debt. A baby wants what he wants now and gets it because he is totally dependent (and loud!). He/she gradually learns how what you want, what you can have, and what someone else will give you, all fit together in the framework of time and life.
If the Bank of Mum and Dad is always open for interest-free loans, never needing to be repaid, there is never any need to learn how to cut his coat according to his cloth, to spend first on the inevitable and eternal overheads and to keep something back for future essentials before splashing out on impulse buys that empty his account - in short, to be a responsible adult.
Get him to enroll in a short course on money management and to make an appointment with an advisor. They can educate him without being overwhelmed with "But this is my baby boy who needs me . . ." feelings to distract you from what he really needs.
As for renting v buying - millions of people rent all their lives and are perfectly happy and successful, with no debts and no stress-related hang-ups.