Download the required themes
First you should download the required two themes which you want to combine and then open the Cascading Style Sheet (CSS) file in the specific web page. Opening the CSS file in a different folder will give you better idea to combine the theme as well. It will integrate with Wordpress easily and you can simply edit it in the web page editor. Overall the names of the themes will remain same but the values might change.
Get information from internet
You can also get information from the internet. There are many websites available on the internet which will certainly guide you regarding combining the two Wordpress themes. Not only the internet, but experienced web developers will also help you find good information about consolidating Wordpress themes.
Installing two themes
After downloading the themes, you should install the two themes using the right process. Check after installing whether it is applied on your blog or not. You can also view your blog in another browser. For viewing the page source, you should first right click on the webpage with your mouse and try to view the page source. Read carefully as you will see the entire coding of the page as well. Write down all the elements which you like most about your applied theme. Write carefully all the elements and then go to your main page of Wordpress and click the dashboard. You then need to active the other theme and repeat the process again. You also need to write all the elements of this theme as well.
Returning to web page editor
Now return to your web page editor and make the relevant changes there. First locate the elements which you wrote down earlier and then using CSS file, combine both themes.