Solicitor Asking For Voluntary Charge On My Property

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Hi, newbie here.
Long story but I owe a solicitor just under £20,000 from my divorce.
It was my intention to pay in instalments at the end of the divorce and they did not disagree with this. However, my expected instalments have been less due to my ex not paying any maintenance as he is not working, so the money I earn isn't freed up to pay more to the solicitor.
I am paying as much as I can at £80 per month and make overpayments where I can, but it is going to take a lot longer to pay off than both the solicitor and I expected.
Understandably they aren't happy and want to secure the debt, wanting me to agree to a voluntary charge against my property.
There is not much about this online. Citizens Advice has been helpful in that they suggest, if the mortgage company agrees to the voluntary charge (I have a small mortgage and a lot of equity - but can't increase my mortgage as cannot afford it) then ensure I get 2 clauses inserted into the charge
1. The solicitor cannot enforce the sale of the house
(Could they do this? whilst they want more per month, I pay the maximum I can and have never not paid them - on direct debit) until the children are 18. By which time I will be pretty much paid up if I continue at the rate I am paying. Though hoping to increase the amount paid over time. (Am really worried about losing my home)
2. The 3% interest is frozen. Though on the statement of account the solicitor recently sent through, there was no interest added?
Has anyone come across or been asked to do a voluntary charge on their property.
Whilst I haven't asked them. I assume if I don't agree they will issue a court summons. Though I cannot pay more, I assume I would get a ccj against me and just continue paying and they could then ask for a charge to be secured for the outstanding amount against my property? Not sure about this side of things.
Unfortunately, I don't have any pennies to get solicitor advice on this. Though might see if there are any solicitors who would give a free half hour advice.
Sorry I have waffled on, but want to hear of anyone in a similar situation or anyone who agreed to a voluntary charge and what happened.
Really unsure if I should go down that route, but don't see I have much option?