I used to be able to send a group text to my son and my daughter in one group text from my Galaxy 5S. Now when I send a group text to them it says "Delivered to Some" . It is always delivered to my daughter's older iPhone but never delivers to my son's iPhone 6. What happened?
Data turned off, that is the reason.
Group texts from non iPhone to iPhone uses MMS texting. Data must be on for this to work. The data used doesn't count against your data allowance, but data must be on.
turn data on, or use another texting alternative, such as whatsapp or Google hangouts. You could also use message plus from Verizon to get the messages when data is turned off And use wifi.