The poops aren't a problem for a child ready to train. If they are aware of their body signals, can give you a heads up and can make it to the potty in time them whether they poop once or 4x a day loose or hard isn't an issue. What makes it an issue is if they are not ready and are pooping in their clothes.
If you don't think the child is ready I would express your concern with lack of signs he is ready. If they insist then make it clear you will give it a try after they do it full in on the weekend and if he has X number of accidents then you will abort until he shows signs of being ready. I wouldn't talk about the poop consistency as a reason he isn't ready. You CAN bring this up after a day of trying and sending home that really messy clothing. Just remove...put it in a large ziploc, seal and send home. They will quickly see the mess and hopefully rethink their position!