Hi Evad.
Does your phone show that the message has been sent, using an iPhone it should always show a progress bar and once it clears that would indicate the message has sent, otherwise you would receive an error message.
Some phones have a "block number" feature, typically Samsung devices.
This can easily be accidentally triggered and you would be surprised how many people get caught out by this.
Although the placement of this feature varies heavily from phone to phone, get your brother to head into messages > options > text messages or possibly applications > block number.
Hope you get it sorted.
