Hi Sherry,
Your question seems to have changed and split into two.
1. Can you buy a house for your son from his trust fund
I'm assuming you are seeking to use the money from your son's trust account, the same money from your late partner's superannuation, to buy this house? If so, this would depend on: (i) whether you are the trustee of the account or not, (ii) terms of the trust, and (iii) when is your son entitled to the trust. Generally, the trustee of a trust can invest this money if it is in the interest of the beneficiary (your son) to do so. This includes using part of it toward a real estate investment. However, the trustee has a fiduciary obligation to act in the best interests of the beneficiary. This means, the investment must be solely in the interests of your son. To show this, you could think about getting some financial advice, valuations from estate agents, renting the property out at market (or above market) rate.
2. The lawyer not answering your original question and "dragging the issue out"
The lawyer should have advised you on fees and costs before retaining you as a client. If not, ask him to give you a breakdown of fees. Did you sign a retainer (agreement to have this lawyer represent you and offer you his services)? You should be firm with your lawyer. Ask him exactly what is going on with your matter, what and why he is doing what he is doing on your behalf, and be clear about what your instructions are. If you want him to pursue a payout from the third superannuation fund, then have the lawyer draft a letter stating that these are your instructions and sign it. If not, write this in a letter to your lawyer. It is the lawyer's duty to follow your instructions and not go beyond this. If he does, you may not need to pay him.
3. What exactly is it that you want from your late partner's superannuation funds?
If sounds like this money is all going to your son. Are you not happy with this? Are you disputing with your son for the funds? Or are you just looking at what you can do as trustee of your son's account?
If you and your late partner separated over 6 years ago, despite being on good terms with him, this does not give you an automatic right to his superannuation fund. In fact, nobody has an automatic right to anybody's superannuation fund except the beneficiary of the fund. If the beneficiary (your later partner) dies, then it goes to the nominated personal representative. If there is no such nomination, then it is the choice of the superannuation fund who they distribute the money to. For this, best to ask for a copy of the superannuation fund's distribution policy.