Settlement agreement...WTF!
From nought to turbo miles per hour or what?
However much time you have had off to look after your sick children AND the business cannot sustain your absence, to get this stage without having directly met or spoken to an HR bod smells off to me.
Settlement/compromise/car park (as they are affectionately known) agreements are a neat pincer move, supported by HR, to get vulnerable employees out. The practical leverage being the employee in difficult circumstances is offered a wodge of money & the threat of dismissal is removed, & in return the employee is no longer under pressure, has a small sum of money but now has NO recourse to discuss further or take legal action.
Any good employer who offers a settlement agreement - because in some circumstances it is a win-win agreement for all parties - will strongly urge the employee to seek legal advice before signing...& it also offers the employee the opportunity to negotiate a better deal. As I say, in some circumstances a settlement agreement can work well for both parties.
Your line manager, I think, sounds like a manipulative arse.
I hope the ACAS call is going well.
Now the settlement agreement has been mentioned, gloves are off.
It is now time to see a specialist employment lawyer to share what has happened in past few years, disentangle what legal protection or adjustments are due based on your parental, MH & any other protected attributes. Then take advice to help you decide if you want to stay to fight your corner as an employee in that company or leave on terms favourable to you. It is they who have brought the settlement agreement to the table, it is time to negotiate.
Do not resign. It’ll screw your self-esteem, finances, claim of benefits.
SIGN NOTHING until you have had independent expert employment advice & slept on it before making a decision.
Also part of a settlement agreement can be for the employer to give you a ‘vanilla’ reference. You have no guarantee of this if you resign.