I have two smart TVs, both 2014/5 vintage, one Samsung, one LG.
How do I connect them to my Google Home?
Is there apps, or need chromecast for each?
What you need to do at this point is just sit down and access all your gadgetry and your home network. Basically your TVs and Google Home all need to be connected in some way to your home network, and at that point they should be able to detect and work with each other to some extent.
What something like a Chromecast does is add wireless networking capability to a TV that has no networking built into it. An aspect to a Smart TV is it
already has integral networking capability, some just WiFI and some both WiFi and an Ethernet port. So adding a Chromecast to a Smart TV that already has WiFi networking capability isn't adding functionality, it's just duplicating an existing feature.
But a Chromecast may be necessary if one or both of your Smart TVs only has an Ethernet port and no WiFi capability. Presumably one or maybe both of your TVs is/are in completely separate rooms from where your wireless router is located so if running a cable along the floor or drilling holes through walls is not a viable option, than this situation does require something like a Chromecast or a Roku. (Also note these will require an open HDMI port on the TV they connect to).
It would be more helpful to know:
-- What are the exact model I.D.s for both of your Smart TVs, to look up what kind of features to determine their WiFi and/or Ethernet capabilities?
-- What kind of wireless router you have. Is it an ISP supplied modem/router box or do you have your own router (and what brand and model is it)?
-- A brief summary of your home's layout, more specifically where both your TVs and your Google Home are located in relation to where your wireless router is located, including approximate distances between each of them and the router.