Yea I believe you can mix oils together... I had the same question a few months ago about Test Prop and Tren Ace, and I found out they were good to mix...
And like Elvia said, try to keep it to a max of 2ml in one spot... There are some exceptions. I did 700mg of EQ in my shoulder, but EQ is pretty smooth so it didn't bother me... Now in that same cycle I shot 500mg of Test E in my other shoulder and until i got used to it that was enough...