No. Exactly we cannot say that Nokia 8110 4G is a waterproof device. But it is IP52 certified. Means it is splash proof. You are protected up to some extent by water.
Yes, Nokia 8110 4G does have the FM radio.
Yes, Nokia 8110 4G is a dual sim mobile phone. You can use one 4G sim card in one slot and another slot will be on the 2G network.
Yes, Nokia 8810 4G does have the VoLTE support. You can make calls via VoLTE enabled network easily.