the sims mobile family portrait poses

Hello there!  I have a question about the different poses for my sims in the family portrait.  What do the different poses mean?  Currently, I have two sims, the wife and the roommate who look to be thinking or are wondering something.  The wife and roommate are best friends.  I attempted to have them hang out thinking their poses would change but they did not.  Also, my husband and wife are not next to one another, the roommate is in between them.  Any insight is much appreciated!  Thanks!

@Ilois4   Yes!  Thank you so much!!!   Changing the sims clothing seemed to make my sim in appear in a better mood.  I also figured out that if you look at a sims profile to see what they are thinking this can help too.  For example, if the sim is thinking of their crush and you send them to work, the sim's expression/mood looks less happy or confused. 

All of my sims live together in one house.  I was thinking of buying a second lot but I don't know if buying a second house will give me two additional open sim slots.  So I am on the fence about buying a second home.    Thanks so much for your help!