Instrument amplifier REF pin current
I have four channel, can I use one AD8541 to set four REF pin voltage
of four AD8422?

Yes you can providing all four AD8422 InAmps require the same voltage.

How much current of these REF pin usually draws?

Typically the input resistance of the REF inputs is 20 kΩ so that's 50 μA per volt.

I'm using ADR423 voltage reference for AD7190, can I use AD423 ref
output and divide it to 0.6V and feed into AD8422 ref pin.

Well, your schematic shows the reference input voltage to be 996 mV so I'm confused here as to what you require. However, if that was resolved then the voltage divider resistance might get significantly loaded by the REF input's input resistance of 20 kΩ and give you errors. It might be doable but the devil will be in the detail. A buffer amplifier is the probably best solution but that also comes with an error budget such as input offset voltage etc..

Did I need to enable the buffer mode of the AD7190 input?

Buffered mode restricts the possible input voltage range and you haven't said what that is so, it's difficult to say whether you can get away in buffered mode. However, buffered mode does deliver a much smaller input current but, given that you are using InAmps as buffers, it seems unlikely you'll get a benefit from using buffered mode.