1 - Depends. If you have an ASIN for a bathroom bin, what you ship should match exactly what is on the ASIN. And if there are other sellers on the listing - then yours would either not be as described, opening you up to refund requests (crazy as it sounds, including additional items to that listed would mean the customer could rightly open up a return request for not as described), or if you went and changed the listing to reflect the free gifts (and I think there are some rules around using the term ‘free gift’ on an ASIN anyway) any other sellers would be at a disadvantage as their bin would not include the toilet brushes.

You could either setup a new bundle that is Bin and 2 brush heads as a new ASIN - but list for the same price as the bin on its own, or you can use the Manage Promotions tool to setup a promotion where if the buyer buys one bathroom bin, they get 2x free of another ASIN. You’d allocate the ASIN for the toilet brush to achieve this.

2 - I don’t believe this is an issue, provided it doesn’t drive the sale off amazon. Amazon Manage Promotions offers the capability to generate coupon led discount codes - so it should be OK.