YOU SAID:

come to sit en a chair

INTO JAPANESE

椅子に座りに来る

BACK INTO ENGLISH

come to sit in a chair

INTO JAPANESE

椅子に座るようになってきた

BACK INTO ENGLISH

I'm starting to sit in a chair.

INTO JAPANESE

私は椅子に座り始めています。

BACK INTO ENGLISH

I'm starting to sit in a chair.