Husband only sibling died, he's struggling mentally, sleeping in his car, irrational behavior is this psychotic behavior?

If this is new and radical behavior for him, it is obviously a cry for help.

I would take him to the nearest emergency room and have him examined by a doctor and a psych exam.  He may need hospitalization or at least a referral for care.

he might just be grieving

I don't think its psychotic... just grief. What kind of irrational behavior are we talking about?