替 (Kanji for substitute)

Onyomi

TAI - you don't need this

The two husbands were TIED together all day - you can't replace one without replacing both of them.

( を ) か＊える	I switch from one thing to another thing - usually of a different type: (switch channels / modes / clothes / sides) ★★★★☆
( が ) か＊わる	something was substituted-something automatically switches (modes/channels/places) ★★★★☆

両替(りょうがえ) する

make change ★★★☆☆ NOKURI
両 (both) + 替 (substitute) = 両替 (make change)

to make change - i.e. "Do you have change for a dollar?"

取り替える(とりかえる)

to exchange ★★☆☆☆
取 (take) + 替 (substitute) = 取り替える (to exchange)

着替え(きがえ)

a change of clothes ★★☆☆☆
着 (wear / arrive) + 替 (substitute) = 着替え (a change of clothes)

Two husbands agree about MONEY (i.e. it is awesome)

but every DAY they substitute one for the other in a game of wife-swapping.

Everyone has a HEEL fetish.