2 JR passes possible?

Hello!
We are visiting Japan next year for 4 weeks. Is it possible to buy and use a 21-day JR pass AND a 7-day pass or is the usage restricted to one JR pass per person?

our itinary will most likely be like this:

1 week tokyo

then a round trip via

kamakura
hakone
osaka (+mt. koya)
okayama
matsuyama
miyajima
hiroshima
kyoto
and then back to tokyo

if there's time left, we'll make a detour and visit these places on the way back to tokyo
nara
takayama
shirakawa-go
matsumoto

So I planned to use a 7-day-JR Pass for our time in tokyo and the 21 day-pass for our round trip through japan. Just wanted to make sure if we could combine 2 passes in our visit or if only one ticket per person is allowed