Do we need to deal with these defects or can we demand legal action if they do not do a full repair?

If you have not done so, you should consider complaining to the relevant city/county departments (in San Francisco, it would be the Department of...

I'm assuming that you are the tenant? If the fire department has cited the property, presumably the citation requires that the specified problems...

How do I regain possession or can I?

If you were actually in possession (you say you had keys, and moved some possessions into the unit, which sounds like possession), and the landlord...

is there anything we can do ?

If you can document a disability (as defined by law), and your doctor, therapist, etc. has essentially given you a prescription for the cats (as...

Won't it be difficult for him to go to court? His unit is illegal. Maybe he's scaring me. Notices are available online.

You probably don't have much to lose by meeting in person, and seeing what he wants. There are several published California precedents...

Is this 30 day notice valid in Santa Clara, CA?

The notice does not have to have a particular title to be valid. However, the contents of the notice would have to comply with applicable law, and...

Can a tenant at sufferance be guilty of a forcible detainer?

It wasn't clear from your post how long ago the lease expired, and whether you did anything (e.g. giving permission or accepting rent) that might...

Serve Unlawful Detainer even though tenant seems to be moving very soon - what are the advantages?

This is always a judgment call. You could see if the tenants (it was not clear from your post whether the boyfriend is also living there) would...

Do I still need a sheriff lock out to reclaim the property ?

Unless the tenant somehow formally surrendered possession to you, and you have good proof (e.g. a cover letter for returning you the keys), it...

I received an unlawful detainer is it valid if it has previous tenant and my name as well?

If the money demanded was not paid within the deadline specified in the 3 day notice, and you don't have a valid defense (such as a defective 3 day...