How do I hide or remove them?

thanks!

It's a little bit convoluted: in the edit parameter interface you have to make invisible the multiparm folder itself.
If you do so, those buttons would disappear from the UI. But also you will lose the integer parm to set the number of instances.

You have to recreate it, and link it to hidden one, in order to add more instances.

addendum: multiparm block list is a very poor performer. Once you have a number of instances, you will easily notice lags in the update of the UI when you create a new instance.

So if you have a lot of istances to add, you might want to find another solution.