You need to isolate the cable traffic from the rest of your coax network. Keep the incoming active drop to your cable modem for internet, but don’t split or otherwise connect the line to the rest of your house coax. Run an ethernet cable from your cable mode/router to the ethernet port on the MoCA bridge adapter, and in turn connect your in-house coax run (I assume that’s the previous Direct TV coax) to the “network” coax port on the adapter. Connect other adapters in the same manner to bridge the signal off the coax to an ethernet connection.
What bridge adapters are you using? Some of them have a built in diplexer, allowing you to attach both the network coax, and a separate coax line to an OTA device, such as an antenna, TV, or Tablo DVR. That works just fine, or you can install a diplexer to do the same thing (IN port connects to the coax drop, SAT port connects to the MoCA bridge adapter, and UHF/VHF port connects to the OTA device). The diplexer splits the incoming RF frequencies, pushing anything above 1000 Mhz to the SAT port, and below that to the UHF port.
The POE filter should be installed on the drop from antenna to where it joins the main coax line- install it on the input side the splitter. It will keep the MoCA frequencies from being transmitted back up to your antenna- but more importantly is that the as the filter reflects that signal, it strengthens the MoCA signal. You only need the one filter, as long as the rest of your coax is isolated within the house. MoCA is relatively robust, and you can run up to 15 nodes on individual cable runs of up to 150’.
If you are going to use a distribution amplifier, look for one specifically designed to be used with MoCA. Many of those will have an internal POE filter built into the circuitry.
I use my house coax system as a MoCA backbone, as I have neither great wifi coverage and no ethernet wiring in a every room of the house, but coax exists in those locations. I have three adapter nodes running, and use an over the air antenna, which feeds signal not only to the Tablo, but also to two other TV’s in use in the house. Bonded channel MoCA 2.0 provides an effective data rate of ~800 Mbps, nearly as fast as Gigabit ethernet, and far faster than what you will realize over wifi. I leverage the coax via MoCA to run two wireless access points, both of which are in different locations than my router, so the coax is used as a high speed back-haul between the wireless points and my router, as well as providing wired streaming service to the TV locations. It all works.