Ghostery/Disconnect are leaner memory-wise than uBlock [1]. That is for their own memory footprint. I do not know how much they contribute memory overhead to web pages though, but I suspect not much. I have never benchmarked Ghostery/Disconnect CPU-wise.
I've dropped ghostery about 3 years ago because, even though it was low on memory, it was extremely CPU hungry, making my (then a little old, but by no mean underpowered) laptop take 3-4 seconds of 100% CPU for almost every page.
[1] https://github.com/gorhill/uBlock/wiki/Own-memory-usage:-ben...