It's easy to have countless stories about your wife and kids on your blog because they make up the bulk of your family life, but there is an entire extended family to deal with as well. There are barbecues at your brothers' and Christmas at grandma's every year.
These are fruitful areas to pluck for your blog, but you have to be careful. You now not only dealing with your own immediate family, but others as well. Your brother may not like you recounting how his little hooligan decided to spread jelly on the walls or that your children mistook grandma's underwear drawer for a hat collection.
You always have to keep other people's opinions and emotions in mind when you're writing the blog. Will what I write be offensive or cause ill will if they read this? Odds are they may never read it or they could end up with it passed around the office. The best way to fix this is to simply ask them ahead of time.
If you see something blog worthy, then ask the people involved if you can put it on your website. If they say yes, then consider it the green light you were looking for. If not, then move one and pick something else. Your blog is important to you, but nothing is more important than family. A funny blog post isn't worth alienating a family member.
It can cause ripples that may take months or even years to smooth over. You can't get that time back, so make good use of it.