Some people pick a subject which they are good at, and stick by it. Others look at traffic-generating keywords etc. I have a personal weblog as well and I mostly blog about what I feel like blogging when I write it. A 2nd and 3rd person started writing for my weblog as well but I have to say I barely find it any good. I'm thinking of splitting the weblog in 3 parts or just kicking them out. The problem is I can't tell them what they are doing wrong mainly because I don't know it either. The main source of visitors is offcourse through google (mainly non-returning visitors). Topic made for related discussion
You should look at the first link in my signature. They provide free niche content for websites, and you get to choose how unique each post is. I have linked them to my Blogger blog and ever since have seen a massive increase in traffic. Also you can build natural backlinks with them for better search engine ranking. I hope they help you.
In deference to the previous poster, if it sounds too good to be true then it usually is. There are no shortcuts to creating a successful blog, that is both unique and linkworthy. It takes a lot of hard work, patience, and perseverance ... contrary to these magic-pill, auto-content article sites will tell you. If the other two bloggers do not fit in with your grand scheme of things, then create new blogs for them ... for free. Let them do the work of writing and you can reap the rewards if they succeed. Either that, or get rid of them altogether and find some people with the same interests who would fit in more comfortably. Keep on, keeping on. Don't stop. Don't look back. Just keep going forward, learn, practice, evolve.
I never thought there was any. And my purpose isn't to get tons of advertising money with this one. It's just for fun and contributing to the internet in my own way. I consider passing my fellow writers their own weblog and connect them in some way.
Do some research to see if people are searching for something and make a website around it. I think pretty much anything is worthy to blog about.