Just ignore them until they say hello to you. Preferably try and start a 'nodding head in greeting' prior to the 'hello' greeting as you don't want to across as overly friendly in case you have to make conversation on a regular basis.
at a previous home I took a tray of tea/coffee and home made biscuits as I thought they looked harassed... start of a mutually beneficial cat/house sitting arrangement that lasted for nearly 3 years
start a loud imaginery argument with yourself when they are in earshot and include references to boundary walls, stabbing, overgrown trees, bodies under the patio etc etc and then take it from there
go round with a bottle of wine and two glasses [ in case they havent unpacked theirs] and say welcome to the neighbourhood, can I help or can I take your kids whilst you get on with the unpacking.