I have a domain name and I created a few sub-domains from it. So it's kinda like this:

productA.domain.com
productB.domain.com
productC.domain.com

The idea is that each of them would be a totally different site with a totally different product. But all under an umbrella of the same company. I kinda want to interconnect all the sites together. I was thinking I would create a kinda "free advertisement" for my sites this way. Like if a potential customer is looking for product A and gets to site A and then he sees the ad for site B with a product B and goes to a site B to buy product B etc.
And I have a few questions or dilemmas to solve.
1) Yeah, on one hand it's cheaper and easier to manage a structure of a few sites together, but how to brand those 3 sites...To try to distinguish them one from another or to try to find a common denominator and to show clearly that all sites belong to the same master or the same source?
2) From a standpoint of visual branding...It's not clear whether I should create a separate logos for instance or not etc. Like how much of a common branding should be in those site that reside on the same domain, but sell totally different things?
3) That kinda "cross-advertisement"...Wouldn't it be a potential distraction for a potential client?
4) Wouldn't it create a wrong impression in client's mind that since you can't be a master in a few areas all at once, then it's probably not a worthy place, since the owner is kinda a "master of none"?

Well, there's always a way to TOTALLY separate (disassociate) all 3 sites from each other. Like to just put all 3 on a totally different domains with a totally different contact infos etc.