I have 2 Wordpress Websites I need to Merge Into One Site

I have 2 websites, both managed under 1 wordpress CMS login, that i wish to merge together into just ONE website in wordpress. Below are the 2 different websites:

https://sexandlondoncity.co.uk/

http://sexandsingaporecity.com/

I need them merged into 1, and then ALL URLS redirected to a new web address: www.nixalina.com

All categories need to remain the same, such as nixalina.com/beauty /travel / fashion etc

All old links need to not be broken, just redirect to new website URL.