Does a husband need permission from his wife/wives to take on another wife.

According to Shari'a, a Muslim male may have four wives simultaneously with
the condition of maintaining equality among all his wives. Therefore, in
principle, you can remarry without divorcing your wife.

However, in order to avoid bitter feelings to your present wife, you should
first discuss your intentions of remarrying with wisdom. That will save you
from the negative consequences fo betrayal, etc. being possibly expressed by
her upon her discovering your secret remarriage.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai