"Part Time" pseudo tenants?

[Sam Leon]

ok have a situation I need some advice on.

2/1 unit with tenants, father on the 50s and daughter early 30s.  Current lease is a single page lease from last owner, with hardly any rules in writing, which I have to live with till July 2015.

Recently I noticed a new vehicle parked outside and vehicle owner has a key to the unit.  Upon further inquiry it turns out to be the daughter's new BF, who apparently has been given a key and stays with her on weekends and sometimes on weekdays.

In my own lease I disallow guests to stay 7 consecutive days or longer so even if they are under my lease, which they are not, they haven't broken any rules because they could technically have a guest for 6 days then skip a day, then 6 days again and be in compliance?  In this case its 3, 4, 5 days per week, or another way to look at it he is there at least half the time.

My issue is first he is not screened, he has a key, he is using water which I pay for, and his car occasionally causes parking space congestion.

I am going to have a talk with my tenant about this, but there is nothing in the lease that prohibits this.  But if he has a key and is present when he others are out, I am going to insist he be screened.  I think I will tell them if they renew in July the rent will jump substantially higher.