I am sorry for you loss. To give the terms and conditions of the Will effect, it must be submittd to the Court for approval and estate musted be probated. You are asking some very broad and lengthy questions. I suggest that you take the the time to speak with an attorney - many offer a free consultation - who can explain the probate process, etc.
I wish you all the best.
I am sorry for your loss.
It sounds like you may have a confused understanding of what is going on. Your sister, as the nominated executrix is responsible for petitioning the Court to allow the Will and to appoint her as the executrix. The process must take place in order to get the authority to distribute assets in the decedents name. Depending on the Court that she is petitioning, the time can vary. Generally, it is suggested that executors wait one year after the date of death, or four months after the date of appointment, before distributions are made. This ensures that no creditors or the state come to the executor for debts owed to them.
If you are not satisfied with the job that your sister is doing and you think that you need independent representation, I suggest that you contact a probate attorney. Otherwise, your sister will need to comply with all the laws surrounding her appointment, so you could sit back and watch to see how things unfold and react if necessary.
There are a number of questions in your post and you need to consider each separately. It is important to know that this is general information and that it may be in your best interests to consult an attorney about your specific situation.
First, does your sister have to petition the will? If there are any assets that were owned by your mother individually and that had no beneficiary designation then, yes, your sister has to open a probate in order to get those assets and distribute them to the beneficiaries. There are different types of probate, and the time it takes in order to be appointed varies but, as an heir and/or beneficiary, you should be receiving notice of what is happening.
How long does a will stay in probate? In Massachusetts, creditors have one year from the date of death to come forward. For that reason, I advise almost all of my personal representatives to close the estate out and make distributions only after the year has passed and an accounting has been prepared, shared with all of the parties and allowed (approved) by the court. If the personal representative distributes assets before that one year, and the beneficiary spends it, the personal representative can be personally liable for paying creditors.
I hope this basic information is helpful. Good luck.