Overseeding Tall Fescue into existing Ryegrass and Kikuyu lawns

I’m new to the program and looking forward to improving my lawn knowledge.
I currently have 1 lawn that is a Wyatt’s quick grow blend (which I believe is a mix of ryegrass, fescue and brown-top) which is fine but doesn’t hold up over summer months. I needed something to fill in the dirt fast after it was a building site. My second lawn is Kikuyu.

I’m looking to overseed in next few weeks and it seems that the Elfin Tall Fescue is a good seed for Auckland, Northland area. Just want to check that it would be okay to overseed with that into my existing lawns without it looking patchy. I don’t have any fixed irrigation.

Any advice would be greatly appreciated.

Thanks.