Father in law likes rye Manhattans and is coming to town...

Since you are going with mixing Manhattans I'd either go with Rittenhouse Rye 100 proof or else (and I am being serious) your basic plastic screwtop Old Overholt. There are more expensive options out there that are good sipping on their own but don't mix as well as the two mentioned.

Drop the extra cash on some quality vermouth, say Carpano Antica sweet vermouth and a bottle of Luxardo cherries. Throw in a bottle of Angostura bitters and you're set. The vermouth is what will elevate the drink and should please your FIL.

if he's a Manhattan man the bottle of old overholt will be familiar and welcome
as above get a good vermouth, angustora bitters, a muddling spoon and a good rocks glass
you'll want to have a couple oranges for garnish and maybe some cherries but I usually leave those out

Lemon twist complements the rye in a Manhattan better than orange or cherries.

Almost everything NumberSix said above, except I prefer Regan's orange bitters to Angostura in a Manhattan. Definitely get the Rittenhouse rye if you can find it.