I agree with the general sentiment here: the rules exist for a reason, so that paying guests get what they pay for, while at the same time, non-paying guests don’t get a windfall, to the detriment of the paying guests. This includes pool use, parking spaces to park the cars to use the pool, and tossing all their stuff on multiple of the finite number of deck chairs adjacent the pool.
Is this likely going to have enforcer employees, grinning ear-to-ear, waiting at the ready to evict the visitors? Probably not. But, like many things in life - - how likely would it be for store employees to catch you stealing a pack of gum at the grocery store? - - it’s the honor code.
That said, it’s not all doom and gloom. I would try to get creative; if your hotel room(s) are not at max capacity, why not add the Ft. Lauderdale family to the reservation in name only, so that they are “guests”? If the rooms don’t have additional capacity to do this, why not ask the hotel in advance - the CMs would likely have a good understanding of volume and usage, and may say it’s fine, or may not. Beyond that, I thought at least some of the hotels (BC comes to mind?) were charging a ‘day guest’ fee.