What is the ruling on the money I previously took in exchange for an increase in commodity prices, and is it permissible for me to take an increase on the prices of commodities that I sell to my brother's customers through my Facebook page?

Firstly: If the salary increase and annual bonus are merely a promise and not part of the contract, then it is not permissible to take anything from the employer's money as compensation without his knowledge. However, if it is part of the agreed-upon contract, then it is permissible to take one's right even without his knowledge if no other means are available. This is known as the issue of "seizing one's right" (al-Dhafar bi al-Haqq).

Secondly: It is permissible to display pictures of spare parts, then purchase them from your brother and sell them to the customer. It is also permissible to sell a commodity you do not own through a salam contract, provided that the commodity's description is precise and the full price is paid at the contract session. It is permissible to act as an agent for the customer, purchasing the commodity for him in exchange for a known commission, or as an agent for your brother in exchange for a commission. This latter scenario is the closest to what you described.