OK, there are only a few things that can be happening here.
1. You are using dirt you dug up from outside which is full of other seeds (elm tree seedlings look very similar to MJ seedlings at that size). It looks like you have potting soil from the pictures but if you mixed outside dirt with your potting soil you could have put all kinds of other seeds in there.
2. You are using VERY bad potting soil that is full of other seeds. I personally don't think this is the case because I have never seen
that many unwanted weeds come from any potting soil I use. Those seedlings also look like either MJ or something that looks like it at that age. They do not look like the normal weeds that I occasionally see come up in potting soil.
3. This is the one that I think is happening. You are either unknowingly planting in soil that you have already put other MJ seeds in, or someone else is putting MJ seeds in your pots when you aren't looking. It looks like I can see a pot seed in the picture you posted of all the seedlings you pulled out, but it's blurry so I can't be sure. If you have friends come over and smoke they might be cleaning their weed & throwing the seeds into your pots without you knowing.
I would recommend that you go buy a bag of Fox Farm Ocean Forest potting soil and plant your seeds into that. Make sure nobody else has access to your pots that might be throwing bagseeds or whatever else into them. Take your biggest MJ plants and replant them into the Ocean Forest soil, they will thank you for it!