I don't believe existing IPs can be moved to NodeBalancer, but I may be wrong. (I've also never known Google to care about IP addresses, but there are some who believe they do.)
And yup, your nodes are (almost certainly) on different hosts. Unless it absolutely has to, the system won't put a new Linode on the same host as one of the Linodes already on your account. This can be verified via the dashboard, in the host information box on the right side... if you've struck the SPOF Jackpot and have two nodes on the same host, open a ticket for one of them to be moved and it will get taken care of.

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