401k funds comingled with other investor cash

[Dana Brash]

Hi all, 

Brand new here. I’m establishing a solo 401k to invest in some flips and eventually multifamily holds. I’m looking at how I can do this in partnership with other investors who will use cash and/or loans.  

I’m told mixed fund types is ok but I’m curious if my arms-length restrictions on DIY work are imposed on the other investors by proxy. Or e.g. can cash investor #2 take on the kitchen? 

Are there any good resource recommendations for learning accounting for a project like that?

thanks so much!

Dana