Am I sinful for buying cell phones that contain ringtones which cannot be deleted, knowing that their owners will use them, and do the angels not enter homes that contain a bell?

Not all mobile phone ringtones are forbidden. Some are forbidden music, while others are ordinary permissible tones. Therefore, there is no harm in purchasing mobile phones for your siblings. If someone uses musical ringtones, they should be advised and informed about the prohibition of musical instruments, and enjoined from this evil. As for house doorbells, their ruling has been clarified in a previous fatwa.