OK, Anna.

I'm going to start by suggesting that you read my tutorial, which describes several possible causes of what you are referring to as "merge and combine".

http://blogging.nitecruzr.net/2009/08/your-email-address-and-blogger-account.html

There are 3 points which I make in that tutorial, and I will enumerate them.

1. Blogger / Google makes it easy for us to (inadvertently) create extra Blogger accounts.
2. When we login to Blogger, we login to a Blogger account - not to a blog.
3. When we login to Blogger, we can be affected by a Google login cookie.

Those 3 points, considered together, will explain why you observe that Google police merge and combine two blogs.  I'm going to suggest that you follow me, as you are not the first person who has had this experience.  These are 3 different articles - each of which relates to one point, above.

http://blogging.nitecruzr.net/2008/05/your-email-address-and-blogger-account.html

http://blogging.nitecruzr.net/2010/02/your-email-address-and-blogger-account.html

http://blogging.nitecruzr.net/2008/10/your-email-address-and-blogger-account.html

I'll ask that you be patient of me - and I will try to do the same, with you.