Can't seem to remove or alter website blocking restrictions on iPhone 6
You are using the new ScreenTime for iCloud (this is different from the local ScreenTime you have disabled). It sounds like the local restrictions on the iPad has been passed on to the limited Apple-ID and then stored on iCloud. The limited Apple-ID has a builtin ScreenTime which stores its settings on iCloud and overrides the local ScreenTime.
There are two ways of controlling ScreenTime for iCloud.

From another iPhone with a parent account signed in with. Open settings app, click on parent name at the top. Scroll down to Family Sharing and select your child's limited Apple-ID. At the bottom you can turn off ScreenTime for iCloud. You may also from this screen change limits (e.g. allowing websites e.t.c.).
From the limited iPhone. Open settings app, click on the name of the child at the top. Scroll down to ScreenTime and select the child name again. Here you can control ScreenTime, but not disable it.

The setting you are looking to change is located in &quot;Content &amp; Privacy Restrictions&quot;/&quot;Content Restrictions&quot;/&quot;Web Content&quot; user the subpage described above.
The name &quot;ScreenTime for iCloud&quot; is a name I made up in order to distinguish with the local ScreenTime in this answer.