Firstly, the establishment of refugee camps for Palestinians in Jordan and other neighboring countries by the UNRWA was a direct response to the 1948 Arab-Israeli War, which led to the displacement of approximately 700,000 Palestinian Arabs. This event, known as the Nakba or "catastrophe" by Palestinians, resulted in a large refugee crisis. The role of UNRWA in providing assistance to these refugees is not a reflection of the lack of "brotherhood" in Islam, as you suggested, but a humanitarian response to a crisis caused by war and displacement. The Palestinians, in general, don't want to leave. They want to stay in the Holy Land.
Regarding your comments on population growth and genocide, it's important to clarify a few points, to help you out. The increase in the Palestinian population over the years does not negate the severity of the hardships they have faced, including displacement, military occupation, and loss of life and property. The growth of a population under duress is a common demographic phenomenon and does not invalidate the suffering experienced by that population.