Yes, you are right. You can only connect to 1 remote site at a time with VPN Client.
However, if you have site-to-site VPN between the 2 remote sites, you can configure it so once you are connected to 1 remote site, the vpn client can also have access to the other remote site via the site-to-site VPN between the 2 remote sites. In this case, you would need to add the vpn client pool subnet to the crypto ACL on the site-to-site vpn tunnel and the vpn client split tunnel needs to include the other remote LAN.
Hope that helps.