Is it permissible to use a Samsung laptop, provided by the company to an employee for work purposes, for personal use such as playing games?

If the company permits the use of the device for personal matters and playing games on it, then there is no harm in that. However, if the company only permits its use for work-related purposes, then it is not permissible to play games on the device, even if your brother permits it. The matter reverts to the employer.