Can I reject this couple's tenant application?

[Mr Good]

I own a single house with two separate residences (separate everything). The upstairs is rented to an extremely nice couple, quiet, they have the garage and much nicer overall setup so they pay $1200/mo. Basement suite is $800/mo.

I met a couple today for the basement unit. She has an air about her which is demanding and bossy, he comes across as Mr Penny Pincher and he looks aggressive. I got a bad vibe especially when he said that right down the street his 14 and 9 year old daughters live, he wants to bbq outside all summer, and use the lawn. The basement suite has 1 bdrm. It's going to be too much commotion to have this guy and his whole family coming over to play football and have bbq outside, when the main floor has to deal with all of them.

Can I reject this guy based on what grounds? Can I say that the basement suite is only available for not more than 2 persons, thus eliminating his kids from coming over, thus making him not want the place?

Hope that makes sense. Appreciate any advice. Thanks!