We have Standard Boiler fitted with Pump upto 4 bar pressure . Will that work for 2 Steam showers that I am looking to buy

Yes absolutely. The minimum we would recommend is 1.5bar for the steam showers to ensure reasonable performance. To enable the jets and a very good flow from the overhead monsoon 2 bar or more would be ideal.

With 4 bar you have very, very good pressure. You may have slightly diminished performance if both showers are in full use at the same time (jets and monsoon in use on both) due to the demand on the pipe capacity more than anything, but the steam function will not be affected.