First time MFR questions.

[Elias Barend Westhof]

So we are about to buy our first property. It's a quadplex in downtown LA, with all units occupied. We intend to move into one of the units. It's unbelievably difficult to get an understanding of what all the current laws and regulations are regarding moving in to an occupied unit. Not even our agent knows what the current rules are. 

Is it possible to move in to one of the occupied units under current regulations? Also, one of the renters has not payed their rent for 6 months as a part of the moratorium. Will they eventually have to pay for those 6 months? Will they pay us or the previous owner?

An additional question: In the contract we recieved, it states: "Seller will provide estoppel certificates as a required delivery item prior to the close of escrow and estoppels will not be subject to any buyer contingency approval. Seller will conduct reasonable efforts to obtain all tenants' signatures on the estoppels but in the event that tenants are unwilling or unavailable to sign, Seller will sign only."

I'm having a hard time understanding what exactly this means, could someone fill me in? 

Lastly, is there any website showing the complete list of current rules and regulations regarding these issues, both in LA county, statewise and federally? Every website seems to state something completely different. 

All answers are greatly appretiated. 
Thank you