Yes. It is safe . Please remember that Pregnancy is a natural phenomenon. Almost 90% of the women will be pregnant at some time in their life. A very large number of them may never have sat on a chair in their life. They all sit cross legged, don't have any check up and investigations during pregnancy  and still they have healthy babies. So you should do what you are used to doing when you were not pregnant Don't try any new posture or position or activities which you were not used to doing earlier.

There are no contraindications as such but if you have pain or any spotting per vaginum, avoid it.

Safe

Avoid sitting on the floor

Safe

It depends on case to case... Without complications ... U can sit on floor with crossed legs... But it's not universal

Safe

Safe