I've never been divorced myself but my parents split when I was young. We would hear them arguing at night for almost a year leading up to it, or sense a very icy uncomfortable atmosphere or our mother crying and angry all the time. Although it was very hard for the first 6 months when they split up, it was honestly better for everyone once things settled down and we adapted to the new normal.
My advice would be if you're not happy please don't "stay together for the kids" although I know you're in a horrible position right now. If you think the relationship can be saved and it's just the pandemic that's added this stress, I'd suggest couples counseling if you can access that.
If not, get your finances prepared and work out an exit plan - e.g place to stay with a relative (if you think they will stay in the current house), if you will stay in the house then see what it would be like covering the bills on a budget for your sole income. (
If that puts you in the red then see if you can find out child support contribution amounts online based on salary, I'm not sure if the exact calculations the CSA use are available but there may be resources to help estimate it.
If you have the income available to save and separate bank accounts then start putting money aside in case you need a solicitor.
Plan the day you're going to tell your partner in advance, once you're ready sit your partner down on a day and time where you're both at your most calm to explain you want a divorce, rather than asking for divorce mid-argument or when one of you is already stressed/angry about something (so not in the morning during the school rush for example).
If you're both calm then hopefully you've got a better chance of working out a divorce mutually, if they're being a prick get the solicitor involved ASAP.
My siblings and I were played against each other and the other parent by our parents, I know it's hard but try not to mention in front of the kids that their other parent is a twit, even if they are a massive twit. Vent to adult friends, online forums or relatives rather than the kids. You're not superman though so don't beat yourself up if you never manage to 100% stick to that, it's inevitable you'll get frustrated in front of them at some point, just don't fall into the trap some parents do of trying to be "the favourite parent" by constantly putting down the other parent.
Feel free to take some all or none of this advice, please do what's best for you. You deserve to have a happy comfortable home to raise your kids in