Yes, Nokia 5.1 is a VoLTE mobile phone.
Nokia 5.1 has an ARM Mali T-860 MP2 GPU. It is a dual core GPU and GPU frequency is 700 MHz.
Nokia 5.1 has a 3GB LPDDR3 type RAM. It is a single channel.
No. Nokia 5.1 has 2 dedicated slots for the sim cards and 1 dedicated slot for the MicroSD card. You can use up to a 128GB memory card in Nokia 5.1.