[SalesForce] remove the approve, reject, recall buttons from approval history related it

You can't customise the buttons on the approval related list like you can for the others.

Aside from Visualforce, you might want to take a look at this post from Jason Venable (aka TehNrd) regarding showing/hiding buttons through javascript:

http://www.tehnrd.com/show-and-hide-buttons-on-page-layouts/

You could then have a roll up summary field on your master record that shows the number of child records that have not been submitted for approval, and your javascript can interrogate that value and hide the button accordingly.

There is an element of fragility about this, as you'd be relying on accessing fields/buttons by names that could conceivably change under you.

Another way to approach it may be to have the approval process entry criteria take into account the rollup summary field of child records not submitted for approval. While that wouldn't stop the button being displayed, it would stop the record entering the approval process.

https://login.salesforce.com/help/doc/en/approvals_recall_actions.htm

This option of recall is available only if you have checked the checkbox "allow the submitter to recall".If you uncheck the recall button won't appear.

And putting your own custom button will imply you may need to write your own approval process using apex classes for approval process.