I'm JS a contributor here. Welcome to the TELUS Neighbourhood!!
When you send text messages that never get received, have you confirmed the correct cellphone number with the people that are not receiving the messages?
If you have entered a phone number that may have numbers in a different order then that message may go to another person's cellphone or a number that is not in service.
FOR EXAMPLE: if you text "HELLO" to 555-555-1234 that person receives the message and then if you text "HELLO" to 555-555-1432 that person DOES NOT receive the message because his/her number is 555-555-1324 there is the solution. The destination phone number was entered wrong.
When you send text messages always make sure you have the correct destination cellphone number of the person you are sending the messages to. Texting can be at times fun but also a tricky thing to use. Just be careful when entering phone numbers as you never know where the message goes unless you get a response from the person on the other end.