I am in the process of remodeling my basement and with that, the bathroom. This 1950's home had a pre-existing bathroom in the basement when I moved in. The toilet that was there is staying in place. I have however, decided to replace and re-locate the sink and shower. The old sink had its drain routed into the concrete slab of the basement, but due to the expansion of the bathroom, that drain cannot be used (it would be located in the middle of the bathroom). The old shower was simply drained, via PVC along the top of the concrete floor, with a few elbows, into the main basement drain below the utility sink. The washing machine also drains into that sink and therefore, into that main drain. My question is this... what problems, if any, will I run into if I connect the new shower drain to the existing PVC and also connect the new sink drain pipe to the same existing PVC. Please bear in mind that I am plumbing-ignorant. Thanks for any help!

I am in the process of remodeling my basement and with that, the bathroom. This 1950's home had a pre-existing bathroom in the basement when I moved in. The toilet that was there is staying in place. I have however, decided to replace and re-locate the sink and shower. The old sink had its drain routed into the concrete slab of the basement, but due to the expansion of the bathroom, that drain cannot be used (it would be located in the middle of the bathroom). The old shower was simply drained, via PVC along the top of the concrete floor, with a few elbows, into the main basement drain below the utility sink. The washing machine also drains into that sink and therefore, into that main drain. My question is this...what problems, if any, will I run into if I connect the new shower drain to the existing PVC and also connect the new sink drain pipe to the same existing PVC. Please bear in mind that I am plumbing-ignorant. Thanks for any help!
You want to drain the lavatory, washer, and shower on top of the floor line into a floor drain?
I guess if you don't really care about code it would work after a fashion. However to be in code you will have to open up the cement floor and tie the lavatory drain into the sewer main.
You may then discharge the washer into the lavatory drain line then you can tie the shower drain into the lavatory drain. That way both the shower and the washer will be wet vented through the lavatory vent. The existing lavatory is vented isn't it? I would not go below 2" on the drain line. Good luck, Tom