Hi Thanos,
You can use any ATF which
meets the N402 specification. I have compiled
a list which I hope will save you a lot of searching!
There are also "universal" fluids which claim to be "compatible" with N402. That's not the same thing as "meeting" the specification and there's no point in compromising by using a "universal" fluid when the true N402 fluids are available.
Yes you can mix two brands, both of which "meet" the N402 spec.
Simon