The Bible certainly urges us to be generous–especially to those in need. The Bible says, "A generous man will himself be blessed, for he shares his food with the poor" (Proverbs 22:9). If your husband's relatives are needy, God may well want you to help them.
However, I doubt if simply giving your relatives extra gifts of money will make them stop envying you–which, from what you say, is their real problem. Your husband is to be commended for his hard work, and you shouldn't feel guilty because he has been successful. Jealousy and envy, however, are very destructive. Envy is one of the sins of the flesh which God condemns (see Galatians 5:21). The Bible also says, "A heart at peace gives life to the body, but envy rots the bones" (Proverbs 14:30).
Pray for your husband's family, that God will show them how harmful envy is. In addition, don't cut them off (as you might be tempted to do), but go out of your way to show your concern for them–not just through any gifts you might give them, but by being generous with your time.
Above all, realize that God has given you everything you have, and ultimately it is His, not yours. Make sure Christ is first in your life, and then ask Him to help you to be wise–not just with your money, but in everything.