Among major banks, UPI works on individual/respective numbers for the following banks' joint accounts:
HDFC, ICICI, Yes Bank, RBL, IDFC, IOB
For some of these banks, UPI PIN has to be the same for both phone numbers but it works at least
UPI does not work on individual/respective numbers for the following banks:
Kotak, SBI, IndusInd, DBS, Federal
For Kotak, joint account holder can pay from Kotak app using UPI after logging in with MPIN (UPI PIN is not asked inside Kotak app for Kotak account after MPIN is entered)