Sednev was a local boy, not somebody who voluntarily left Tsarskoe Selo to accompany the Imperial Family. He only started to work for them when they got to Ekaterinburg.
On the contrary, Leonid Sednev did work for the imperial family in Tsarskoe Selo. He was an orphan living under the care of his uncle, Ivan Sednev, the grand duchesses' footman. According to statements made by Kobylinsky, Gilliard, and Volkov, Leonid Sednev accompanied the IF to Tobolsk, and was part of the retinue that was transferred with OTAA to Ekaterinburg aboard the Rus
To my knowledge, no locals (aside from guards and clergy) were permitted inside the Ipatiev house.