Without knowing more facts, one cannot say for sure. But it seems probable that the leases are merely a device to get around the 119 and 135 regulations. If that is the case, the "leases" are illegal.
O-line mentions 91.23, but it should be pointed out that this applcable to Large aircraft. Are large aircraft involved?
That apart, the FAA knows the difference between a legitimate lease and one who's sole purpose is to circumvent charter regulations. They look at several criteria: Does the plan and pilot come from the same source? Can the lessee use any pilot of thier chosing, or are they required to use a pilot from the lessor. WHo has actual operational control of the aircraft? It is not enough that the lease states the lessee has operation control of the aircraft. If the aircraft remains in the lessors hangar, and is dispatched on flights at the lessors discretion, the lessee does not have operational control of the aircraft, regardless of what the lease says. There's no one single determining factor, but the facts of the situation as a whole are examined.
If the Lessee does not have exclusive use of the aircraft (no other "lesees")
and the lessee is required to use pilots from the owner's company, and if where the airplane flies and when is primarily dictated bu the owner, it is almost certinly not a legitamate lease, and the owner could be in deep doo-doo.
Here's a link to an NTSB decision involving a "lease" arrangement. It disusses some of hte things which are examined in determining if a lease is an actual lease or a sham lease.
http://www.ntsb.gov/alj/O_n_O/docs/aviation/4825.PDF