Dropped connection - Netgear Nighthawk ax4200

I will be the first to admit I'm quite technologically challenged... we've had issues with internet since both my husband and I started working from home, so much that he loses his VPN connection multiple times a day. His office is a separate room outside the house, still attached, but separated by a main wall as it used to be the garage. We also have several echos, tablets, 2 fire TV, nest thermostat and doorbell, and about a dozen smart lights all connected to the wifi.

To try to solve the access issue, we purchased a Nighthawk AX4200 dual router, simply because we didn't think the one century link provided was strong enough. Before we got a chance to set up, we also received a 3 pack of the Linksys Velop mesh wifi system.

Current set up is Nighthawk modem/router is connected to the internet cable. Husband connected the velop and one is connected to the router, the other is in the office and the third one is in between. All in the main level, house plan downstairs is about 2500 sq. ft.

Question is, how do I know what the best set up is? I think one may need to be set up as a bridge but not sure which and honestly don't want to mess with it anymore. Thanks for helping!