What is the possible way to have create multi-field RTE in content fragment models (AEM 6.4)

We are trying to create composite multifield's as data types within content fragments to address some of our business requirements. The challenge here is we need to enable RTE plugin-in's for some of the text within multifield and not able to do with OOTB or custom implementation. Here is what we tried,

1. Tried using resource type granite/ui/components/coral/foundation/form/textarea from the dialog which is referred from custom implementation but RTE plugin's to style the content is not available here.

2. If we try using resource type dam/cfm/admin/components/authoring/contenteditor/multieditor within our custom multifield it doesn't work since it's out of cfm

3. Tried using resource type cq/gui/components/authoring/dialog/richtext from the dialog which is referred from custom implementation, RTE plugin's works here  to style the content but the content is not getting stored or retrieved and throwing below console error.

impl.js:1148 Uncaught TypeError: Cannot read property 'setDisabled' of null
at instanceGenerator.updateState (impl.js:1148)
at instanceGenerator.updateToolbar (richtext.js:5021)
at instanceGenerator.updateState (richtext.js:48108)
at Object.fn (richtext.js:2646)
at instanceGenerator.fireUIEvent (richtext.js:4876)
at instanceGenerator.onEditorEvent (richtext.js:4132)
at instanceGenerator.keyup (richtext.js:3673)
at task (richtext.js:1433)

Kindly suggest us some solution as we are stuck on this solution.