Is what is given to a sister, such as seasonal gifts and the like, considered undeserved, especially since the money comes from her brothers' work on the land? And should she return this money? And are her brothers not allowed to pay for the costs of furnishing her apartment in the new house?

First: If what your brothers receive as a monthly and semi-annual salary is equivalent to the customary wage for their work, then what they give you as a gift is permissible to accept. However, if what they receive is more than the customary wage, you have the right to half of the surplus or to waive it.

Second: Your brothers furnishing their apartments is likely not from their work wages, but rather from what exceeded it, and you have a right to a share in it. There is no harm in them furnishing an apartment for you, and if you take a share equal to that of a male heir, you must compensate them unless they consent to the increase. The inheritance must be divided promptly after death unless everyone agrees to a delay. If the adult, sane heirs mutually agree on a specific division, there is no harm in it.