I am setting up 2sites with 1sub-domain right now;
1) Singapore Shop 360 (sgshop360.com)
2a) Directory Singapore 360 (dsg360.com)
2b) Listing Listing Site (listing.dsg360.com OR dsg360.com/listing)
As you aware, these 2.5 sites includes both "SG" and "360" wordings too, hence the design should be the same or similar.
For the part 1, I have attached 1 of my temporary logo for you to review, please take a look of it.
For the part 2a & 2b, the logo look should not be have any big different, maybe can add some sign to identify the differences.