Yucky dark water fills up my laundry tub every time kitchen sink gets used and I've tried to use a cleaner or draino thing to unclog it but no luck any suggestions as the sewage smell is awful please help

You have a clog much further down stream than the tub and kitchen sink. Stop with the chemicals because you need to open the system to rod. Is this a two story home or what, first floor toilet would not back into a tub like this

Bob's "bang on"! You have a blockage downstream from the laundry tray.
The solution would be to snake the line and clear it.
This can be done from one of several places.
1, Snake from the laundry tray roof vent.
2. Remove the laundry tray trap and snake from there using a drop head anger tip.(see image). **OR**
3. If there's a cleanout on the stack you could snake from there.
Good luck. Tom