depends.
a 20% BB content should help the oils mix, if they're different oils.
I always use the same oil for all my products, as do a lot of other ugl's.
I prefer grapeseed oil, and I use 20% BB for all my mixes regardless of the concentration. 200mg deca, 400mg deca, 250mg enan, 400mg enan, 300mg eq, 200mg tren, 200mg masteron, ect... so in theory, they'll all mix very well.
you can always check and see how they mix by seeing how they mix in a syringe. putting 1ml each of your test, nandrolone, tren, ect... leave it over night and see if they oil's sit on top of each other.
overall, I don't think it's a good idea... reason being, I want to know exactly how much of each drug i'm getting, and that number may vary week to week... some weeks I may want to back down on my tren intake and increase my test or increase my npp... of mast, ect..
if everything's mixed, there's no way of playing with the dosages.