There really is not enough info presented.

If this is a community property State or not, makes a difference.

If the property is titled to the partnership, there might not be any provision for step up of basis, since the property is by definition outside of the estate.

The partnership share/value is passed through the estate or per the partnership agreement. The new partner doesn't simply step in and take that place. There was no buy in?

I found a few articles for you, and this looks like a good place to start knowing what answers you need:

https://hmbtx.com/step-up-in-basis-for-assets-held-in-an-entity/