Does Spark Double on Muldrotha allow for additional plays from the graveyard?
Yes, You may play additional cards for each Muldrotha you control.
From the Card specific rulings in Gatherer:

If you play a card from your graveyard and then have a new Muldrotha
come under your control in the same turn, you may play another card of
that type from your graveyard that turn.
If multiple effects allow you to play a card from your graveyard, such
as those of Gisa and Geralf and Karador, Ghost Chieftain, you must
announce which permission you’re using as you begin to play the card.

This is written under the assumption that you can only control one Muldrotha at a time, but it remains true if you control multiple Muldrothas. Each instance of Muldrotha only checks if you already played a permanent of the same type with the permisssion of that specific Muldrotha.
You may still only play one land per turn unless another effect states otherwise.
To be precise the rulings mention multiple effects, this includes other effects as well as multiple instances of the same effect. You will still have to announce which Muldrotha you are using for each card played.