If for parent stick to yoodo their coverage is okay one .Fyi mysejahtera don't need data also can use one it will take the app abit longer to figure no data and manual load the app ( got data instant load ). Tng is another story , for payment to go through yr phone need to have strong data connection else payment will fail one ( I kena with yes at setia Alam mall tng work can show code for cashier to scan but keep fail until I use umobile to share data to this phone only payment can go through).

TnG (using showing QR code / pay function) and MySJ does not require data connection actually
make sure you have enough $$ before give it

I would suggest those hotlink 365 data would be good for your parents as long as they won't surf fb/tiktok/youtube using data outside