As long as Emily's home, you can't do anything with Brenda.
You have to wait until Emily is at college. Generally Emly is at college from 8:00 till 14:00. At 15:00 she at the pool.
So you need to avoid to have Emily at home.
There are 4 days that i do not see Emily at home and that's when she is at college: Tuesday, Wednsday, Thursday, Friday that you can use to do the everythings. In this case the "blowjob"
Generally you can see Brenda alone around the pool (couch) at the 14:00. If she is at the hot tube or in the pool, just change zone and return again in the pool zone. If she is not on the couch, again change zone and return. Believe me sooner or later you will find Brenda on the couch. (this is the best way to find every character, just change zone and return, soon or later they are there). At last in me game, i change zone, return, change zone, return and i find her.