Between the siblings, they decided one brother was going to move in and buy out the other 2.

(Still not exactly sure where that leaves the other sibling's inheritance, and honestly, I'm not too sure that there is a clear answer for that.)

In your position, maybe starting by communicating your ideas to the 3 siblings tied to the property would be a good place to start?

The property is in a trust and has been passed down to share between 3 siblings.

My siblings and I stand to inherit our father's house in Santa Clara County, CA. 

I am inheriting a property in CA with my siblings, the property is in an irrevocable trust and I am looking to buy them out.    

Sibling transfers can be challenging especially with Proposition 19.  

You need an appraisal from date of death because you get a step up basis at death for the capital gains.Do you or any of your siblings want to live in the property.  

As far as I can tell every HOA document has something like this one form or another:The term "single family residential purposes" also shall be defined as: (1) one or more persons related by blood, marriage or adoption, which may include only parents and their dependent children, siblings, parents or grandparents; or (2) by no more than two unrelated persons living together as a single housekeeping unit and their dependent children, siblings, parents or grandparents.See Article III Section 3.1 here as an example: https://1drv.ms/b/s!

You don't want to get the place looking good and find out there is a long lost sibling with interest in the property.