Can cured lymp node TB (koch's lympadentitis) cause infertility? Will it relapse during pregancy& will fetus get infected with TB even after treatment

Not really. lymphadenitis after treatment should not cause infertility if ovaries and tubes are not affected by tuberculosis after successful treatment you may have a normal pregnancy and normal baby.
No, no and no. if TB infection of the lymph nodes (Koch's Lymphadenitis) if it was properly treated and the mother is no otherwise immunocompromised then there should be limited chance of either relapse or transmission to the fetus. (See previous answers. )