The one thing a beneficiary normally has is the right to know exactly what are the terms of the Trust and what the assets are - you may not have many rights, but you do have those. Nobody can deny you those rights, so you should find out both those things, if you have not already done so. If you meet obstruction, you should immediately suspect that something is not right, and be on your guard.
When you know what the total Trust assets are, and the Trust terms, you will be in a much better position to assess whether a "lump sum offer" looks attractive, reasonable, or otherwise, and why any such offer has been made in the first place. Only then can you assess whether you should even consider such an "offer", let alone accept it.
You need a proper lawyer, who understands Trusts and settlements - and, dare I say, such people are not to be found in every small town. Good legal advice is expensive, but it is worth it every time - there's nothing more expensive than a cheap lawyer.
Good luck.
