Oci taxation

I am British citizen married to Indian citizen and I hold an OCI card as his wife. I have NRE and NRO accounts in India. I have moved money from UK to my Indian NRE accounts wanting to invest in mutual funds and buy property at some point. We are mostly in India so my tax status is resident only but I have so far not filed as I am not working and have no income in India. I have a PANCARD and my kyc is done but I have not made any investments so far in India. I do have rental income in UK for which I file tax in UK. My questions: Is it legal requirement to change my NRE and NRO accounts to resident accounts? If in future I decide to move back to UK will I be able to repatriate my money from resident account? Is it possible to live in India, hold nre account and file taxes as resident? Do I need to file tax on UK income in India if I am already filing tax in the UK? My main concern is repatriation in the future and mutual fund redemption because of change of bank account from nre to resident and vice versa. Can tax filing as resident be done without having to change bank account type again and again or it is mandatory to change bank account? I there an easier way to invest in mutual funds?