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For me, casinos are cheating people with this clause. If they detect the same IP by different users, they shouldn't automatically conclude it's the same person, they should have done their homework to know their gambling behaviours which can only truly confirm their guilt or a mere mistake. To worsen the matter, they will now confiscate the money, I wonder which right under the law gives them such power. No wonder the court sides with the customer if the money involved is big enough and the customer was able to file a lawsuit. Unfortunately, most times, casinos go away with the money since most customers are voiceless and powerless.
Same here, the IP shouldn't be conclusive proof anyhow, most ISPs don't even provide static IPs anymore and since most people gamble from mobile in crowded cities it's nearly impossible to not have collisions, but I still don't think they ban only on IP, after all, you have far more important things like the browser fingerprint and the device, not even talking about real methods to detects cheaters, one of he obvious one being KYC!
As for funds, depends, won amounts while cheating? They would be in the right to confiscate if they have proof, deposits should not be touched and returned!
Without going into the question of whether it is an unfair clause or simply to protect the online casinos themselves: knowing that this is a practice that is usually forbidden, and before taking all the trouble to contact the team and explain the situation to see what they think before gambling there, why not simply choose a different casino? like the father plays at xxxxxx.com and the mother at yyyyyyy.com?