In my case i’ve / and /swap.
My /var is about 2.4 Go with this command
du -h /var
It would be better to contact YunoHost dev’s team in order to ask them the efficient size for your /var.
Maybe fix the new size at 6 Go could be enough but i’m not sure of that.
Note that to reduce and move your /home this will take a lot of time due to the 308 Go used, unlike for your /tmp and the resize of your /var they should be quicker.
My first advice would be to have a look into what’s taking place and what you can gain. For instance, maybe clearing apt’s cache might allow to get some significant free space :
apt-get clean
If not, have a look at what’s taking space, so for example start with :