It depends. Room size, room acoustics, and setup are are big factors. The specifics of speakers in question and how they play in your room are more critical than whether they’re floor standers or bookshelf IMO.
Two subs help smooth out room nodes, and you can do more experimentation with placement. Depending on the subs, there are usually lots of options for the low pass crossover frequency, gain, and phase.
I prefer to set the crossover frequency of subs at the lowest setting, run my main flloor standers full range, and set the gain of the sub very low. YMMV, but I hear a lot of subs that have both the gain and the crossover frequency set to high. IMHO it’s best not to feature the subs, but to let them just augment the bass your main speakers put out. Experimentation is the key.