unclenedsfishfactory.com

First off my Yellow Lab has been shaking lately. Should I be worried?
depends,
is he scratching on the gravel? If he is he might have parasites, if it's parasites...change a good amount of water, stir gravel first...add back new warm water with a total maximum of 2 teaspoons of salt per gallon and possibly some medicine such as clout...
if he's just shaking...
healthy Mbuna often display to each other by waggling their fins at each other

Also what is better for my Malawi Mbuna tank either sand or gravel, does not matter

would I be also be able to mix some haps in there also.
yes

Are those the peacocks?
"Haps" is short for Haplochromines
which include Copadichromis, Protomelas, Otopharynx, Nimbochromis and many other genuses

"peacocks" is a common term for the Genus Aulonocara

Mbuna, Peacocks, and Haps are all from Lake Malawi and all like the same alkaline clean water...
but each species has slightly different aggression levels...
basically, the bigger your tank is the more types you can mix safely

as far as which go best with which, it's best to keep a list with your species names
naturally their are a thousand combinations

Lastly is investing in a test kit for the tanks water really worth it?
yes, we like the 5-in 1 test strips