I will guess that you are
The Ace of Hearts in a deck of cards
Confined with my brothers
A deck of cards is often kept in a closed cardboard packet
Occasionally I see Light
Although if someone wishes to play a game, they take them out.
Sent to amuse others
Cards are used to play games
For I don't have any life
Cards are inanimate objects.
Can't see because Eyes is what I don't have
Some cards could be said to have eyes but most don't, particularly the Ace of Hearts would not.
Its the matter of hands but I lack that
Cards are dealt into hands but do not have hands.
God showed some Mercy by giving me heart
The singular here makes me think that you are the Ace.
Make a guess and tell what we are.
A deck of cards