|Are we sure we are talking vpn and not vlan?|
"I don't want to run my entire home network through the VPN, only certain devices."
is not a description of a vpn but of a vlan
another clue is there is no mention of what the vpn is connecting to on the other side of the internet.
technically, as long as the main router supports vpn passthrough and the 2nd router can create a site to site [router to router] vpn tunnel thru the internet, this is entirely possible.
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