Your mother's testament will is unfair and unjust, and must not be implemented thru. The heritage shares are as follow :

The quarter goes to the husband and the rest is divided upon children at the rate of every boy gets as twice as what the girl gets.

Your father has no heritage because he is still alive therefore what he gave to your brothers under a sell to buy contract is regarded as a bounty. Whatever your mother has left is classified under heritage and has to be shared among you according to heritage rules,  whether it'is a ring or one million dollar, unless your siblings agree to offer it to you.