Bad AI?

Sims have things that they like to do, despite what we want them to do and areas with a lot of options means they are going to navigate to the things that they prefer over what WE want. Just like real people, we can't always force sims to do what we want when we want. It can be frustrating but at the same time, it's realistic. Your sim's friend was not interested in the hot tub or drinking at the bar. Perhaps next time, find out what your sim's friend prefers to do and do that instead. And hide all computers. Sims almost always gravitate to those damn things. 

In terms of choosing where to sit, if the outdoor chairs have a higher comfort rating, they will sit in those chairs over the ones inside. 

Also, make sure your autonomy is on - that could be why they just stand around? It could also be that they don't have things around that they like to do. You might have activities in your home, but maybe your sims don't want to do those activities so you may need to make sure there is plenty of things that interest your specific sims. 

To give you an example, my current gen of sims: one only likes video games, playing chess and working out, the other will only garden and I can't get him to play chess for more than a few seconds (which is annoying because he is going to need logic for his career soon), and the other one just likes to cook and socialize... seriously, all she does is walk around talking to the other sims as they go about their activities and I can't get her to do anything because she has the lazy trait and just complains. The one who likes to garden, goes straight to the garden after work, followed by his wife so she can talk his ear off about her day at work (I assume). Her father goes up stairs and either plays chess, video games, or runs the treadmill (sometimes he'll do a little of each before bed). This is all done autonomously.