If you look on Googlemap you can easily find 18 Lydia St. I'm finding 324 Nicholson St a bit trickier - there seems to be a 324 Nicholson St EAST Brunswick but when I look on the street view the house shown appears to be no 69. There is also 324 Nicholson St in Carlton which is now a nicely renovated upmarket terrace house.
Nicholson St is a long busy street, running through number of inner Melbourne suburbs and I would think that the numbering of houses, and even of suburb boundaries, may well have changed over time. The Brunswick section of Nicholson St has much modern building among the older houses - small office blocks, show-rooms, apartment blocks etc. I also note a couple of houses in the area which look as though they may have been built in the 1930s or later.
18 Lydia St looks very nice with the touches of white painted bricks, ironwork lace on the porch, and a bit of a pediment.
Judith