I believe they only care about concurrent IPs, not concurrent use in general. If the IP is the same for all downloads then I don’t think they’ll send you a warning. Just make sure the VPN clients have a killswitch though.
They go by a ‘2 strikes in a week’ system to account for accidental misuse. If they see 2 IPs used at once then they’ll reset your API key and tell you they’ll block your account if you do it again in the next 7 days.
I pay for 2 accounts personally because it’s still far cheaper than watching things ‘the proper way’.