Is it permissible for a person to bring goods for his friends with the aim of profit, knowing that the friends do so for his benefit?

It is permissible for you to buy goods and sell them to your colleagues at a higher price by way of Murabahah (cost-plus profit sale), just as it is permissible for you to buy them for them in your capacity as their agent for a fee. There is no objection to either of these two matters.