How do I remove trap from 50 year old sink to rid of sewer flies

I have tried to snake out the stopper area with plastic snake which is very effective--Stopper does not open or close. I have used a biogradable product to clean the lines. Now I see the overflow holes are crusted and maybe that's why the substance didn't work. This old sink is so tight on the trap area I cannot budge it even with a wrench. I feel like I'm losing a battle with this old sink bu can't afford a new one. Any suggestions would be greatly appreciated.

I live in Florida and every spring when weather warms up I have this problem.

I am a 71 year old widow who has maintained this house myself for 33 years but this problem I can't solve.

How do I remove trap from 50 year old sink to rid of sewer flies