Is it possible for there to be a connection between seeing people in white or seeing a deceased person in a dream and the occurrence of deaths, as in the two incidents mentioned?

It is permissible for some people to see angels, as Gabriel appeared to Mary in the form of a human, and angels came to Abraham and Lot in the form of men. They did not know they were angels until they revealed their true nature. Angels can be seen in waking life and in dreams, but it cannot be definitively asserted that those one sees are angels except through revelation from Allah. Abraham and Lot did not realize their true nature until the angels informed them, so it is even more likely for others not to realize. Nothing is built upon visions and dreams; they are merely glad tidings. Therefore, one cannot definitively assert a connection between the two visions and the mentioned deaths.