What is wrong with this setup?

Here are a couple pictures of the sewer lines in my dad's crawlspace. We are having a debate about venting. The shower drains into the line coming from the washing machine stand pipe. There is a vent on the roof above the laundry room which also has a shower in it. From my understanding you cannot use the washing machine line even though it is vented as a vent since when the washing machine is draining it could siphon the trap on the shower dry?

The second photo shows the line coming from the bathtub which only has a S trap on it. My dad says since it is so close to the main stack the main stack will act as a vent. I don't believe that works since the main stack has the toilet draining into it.

It seems you already know the answer, but if you need to hear it, neither of these would be approved under current code.

1. Cannot wet vent the laundry. Standpipe trap should be above the floor too.
2. An S-trap is no longer permitted. A tub vent could be connected to the stack, but only above the flood rim of the highest fixture on the stack.

It does not matter how "close" to any vent an "S" trap is, it is still not vented. It is like saying your milk should not spoil if it is on a table next to the refrigerator. You are correct about the washer's water velocity possibly creating a venturi effect and siphoning the shower. Whether it would actually happen depends on many variables, some of which are dynamic and continually changing.

My dad recently moved the laundry room to the addition. He always thought the nasty smell in the old laundry room was the washing machine door seal. It smelled more like sewer gas to me. Now that the washing machine is out of there the smell is gone. He plans to turn the old laundry room into a second bathroom. Thanks for the replies.