Can I trade more than 4 stocks per week equally split between two brokers without “pattern day trading” problems?
No, if your brokers find out about this, even though it is unlikely, you will be identified as a pattern day trader. The regulations do not specify a per broker limit. Also, it's like a credit history.  Brokers are loosely obligated to inform other brokers that a client is a pattern day trader when transferring accounts.