I think the number of people will decrease, but I dont think it’ll be that much
I think the amount of people will go down, but not by much
人数 - number of people
減る - go down, decrease
人数が減る - number of people go down, number of people decrease
〜〜と思う - I think
そんなに多くない - not that big, not that much
I think the number of people will decrease, but I dont think it’ll be that much
I think the amount of people will go down, but not by much
イギリス 
