1) Lemon juice can be used (good for cleaning limescale from taps too), and it is supposed to kill them if they come into contact with it, so is a good replacement for any poisons.
2)A home-made trap to use is to fill a glass jar with any of the following: flour, dried cereal, small pieces of bread, starchy food etc.
Wrap masking tape around the whole of the outside of the jar, to enable them to climb up it and get inside the jar for the 'bait'.
Place the jar(s) in areas where you think they are hiding, and check the jars regularly.
3) Baking soda. I know you have tried this with salt but maybe you need to do the following:
Mix a bit of baking soda, a cup of water, and a tablespoon of honey, into a bowl. Mix it all together to form a paste. Put some of the paste on a piece of card or paper to lure them into a glass jar.
4) Put some rolled up newspaper, dampened with water, onto a plate and leave it overnight where you want to trap them. The moisture will attract them. They will climb inside the newspaper to feed and take shelter. In the morning, throw the newspaper in an outside bin.
On the subject of moisture - which is what attracts them, as well as food - do you have a dehumidifier you can use if the rooms have excess moisture in the air?
If possible and safe to do you can check behind appliances, as creepy crawlies like dark, undisturbed corners to hide behind.
Finally, as you mention using poison I am guessing that you do not have any pets, so this is more a warning to others reading this - be careful using any essential oils or poisons if you have pets and/or children around. ALWAYS READ THE LABELS FIRST, and if you have any medical conditions, check that the products are not ones you have to avoid ie I think tea tree oil is not good for asthmatics?
Sorry for the long posts, hope some of it helps