What rights to a beneficiary of the estate have in regards to the decisions of the executor?

Normally, a beneficiary has no right to control the Executor's decisions. The Executor's job is to ensure that the estate is administered properly and that the interests of creditors and other interested parties, including, but not limited to, beneficiaries are protected. As for your other question, however: if the spouse received a check directly from a life insurance policy, that money belongs to the spouse, not the estate, and the spouse is not required to pay for the funeral with that money. Same with Social Security benefits paid to the spouse: that's not the estate's money. The estate is required to pay the funeral expenses, not the spouse, and so if an asset was paid directly to the spouse as a beneficiary under a life insurance or from Social Security, the spouse can keep that money if he or she wants to keep it.