A house was left to me two brothers and one sister 25% each. Are there people who would buy my 25% ?

The will states my sister can live there for life (if she wants to) Long term investment?

Someone will buy anything, it is a matter of how much it is worth. I am sure you have already looked to the obvious, your brothers and sister. If one person were to buy all of the remainder interest that would be worth much more. Alternatively, if all 4 people wanted to sell the remainder interest (that interest which is left after your sister lives there for life), it would be much more valuable. People obviously want to buy property free of entanglements. In this situation you have a lot of entanglements which will lower the value tremendously.

Possible. Your sister retains a life estate in addition to her share of the property that will extinguish on her death; someone might be looking for a long term investment; but since there will be 2 other property owners, I think it'll be a very tough sell.

I would make my sister buy out my 25% since she's the one who lives ther

It would be best if your siblings could buy you out. There are companies who buy part equity in a house but I really wouldn't recommend it. They might slip some sly clause into the contract that could cause hell for you all later.

Your best option would be to try and persuade your sister to buy you out so that she owned 50% of the house. She should be able to get a mortgage to buy your share.

Obviously this will require surveyors reports etc and fees but that is the safest way of getting your money and ensuring everything is above board and legal

Since you own 25% you legally can live there as well. Also you can sell your 25% and that person can legally move in there too, so if you and your brothers want to sell then it would be in your sisters best interest to sell too.

whats the point of owning 25% of the house with 3 other people? how would one be able to prove they own that portion (unless its a multi family house with other units) i doubt anyone would want to touch that mess.

I presume it was one of your parents who left the house to your brothers and sister. They obviously wanted to make sure she had a home for the rest of her life. Please respect this wish, I have been in the same place as your sister and gave up my rights due to pressure. Do not do the same, you should instead think about your sister. By the sound of it your parents thought you would manage without living in the family home.
Let your sister enjoy it, your parents have thought of you as she has only a life interest.

If you need to raise money your 25% of the equity can be used as quollteral if needed.