The antenna Can Not be connected to any active Cable system coax.
If a coax has any type or kind of active Cable delivered service be it , cable Tv , cable delivered internet service , cable phone service , or any other type or kind of active Cable services.
The antenna and the antennas coaxes can not be connected to it.
Do not mix the Tv antenna channels and Cable services on the same coax.
Coaxes that are not being used for Cable services , can be used for the Tv antenna system.
To distribute the Tv antenna channels to the 3 Tv's use a Channel Master CM 3414 distribution amplifier.
http://www.channelmasterstore.com.
The coax from the antenna will be connected to the input of the distribution amplifier.
Coaxes will go from the outputs of the distribution amplifier out to each Tv location.
It is Ok to use coax that is in the house now , if there are no active cable services on the coax.
And what does one do with a coax so the coax has no Cable delivered services.
Easy , disconnect the coax from the Cable system.