A: Family members legally hire family members all the time. There are many small businesses run by families for example. A company might have an internal policy that prohibits hiring a family member. Employees can check with the HR department in their companies to see if that type of policy exists.
A: You should contact the landlord and explain that you paid the rent in full and find out why they posted the notice. It sounds like there might be some type mis-communication or error. Perhaps they misfiled your check, or it was lost in the mail or something. It is best to communicate with the landlord rather than ignore the notice.
A: In most states, including, California, you do not need a lawyer to purchase a home. In some states a lawyer is required for some aspects of the deal, such as preparing the purchase documents, running a title search and closing.
Buying a house is a complex transaction and for most people the largest purchase they ever make, so having the help of an experienced real estate agent or lawyer who is familiar with the process is helpful. Real estate agents are generally paid by commission. The seller usually pays the commission to both the buyer and seller's agents. Lawyers are usually paid an hourly rate for this type of work.