Hi
I have sympathy with you. There's so much pressure to be over the moon at motherhood 24/7 if you've had IVF.
Try (CBT-style) to be a bit rational in your assessment of your situation. You're knackered at weekends. DC are clamouring for your attention as they've not had it all week. No wonder you feel stressed, grumpy, overwhelmed.
I also had two in close proximity via IVF and gave up a career I adored which led to a lot of distress, and I had severe PND. But here's some things I did that really helped me. Life changing stuff for us which I hope will work for you.
When they are demanding, turn the tables. Love bomb them. Keep demanding their attention, asking them questions etc. Don;t let them out of your sight. Follow them around. All for about 20 mins. They might suck it up at first but after a while they get bored. They realise you're there and trot off to do something else.
Try Positive Parenting techniques. Whether or not you believe parenting skills can be learned form books - this stuff is clever, and it's stress free. Make two cosy areas in two different rooms - cushions, blankets, cuddly toys, books, a drink. If they squabble, separate them and say with lots of sympathy: Oh you seem sad. Have a cosy snuggle until you feel better. Then tuck them in and tell them they can each get out of the cosy corner as soon as they feel happy and soothed and able to play nicely. That way there's no tantrumming and sulking about being punished, and best of all they learn to self-soothe and calm themselves down. In our house tantrums evaporated overnight and we went from being stressy screamers to one of the calmest families I know.
Separate the weekend into four hour chunks. One chunk on Friday night, four chunks on Saturday, four chunks on Sunday. That gives you nine blocks of time. Divide them up so that each adult gets a one chunk of time all to themselves, to lie in or go shopping or to the gym or to watch a match. During this time, the other adult has sole charge of the DC, and promises not to let them interrupt you. If they try, the adult in charge takes them out to the park so the other one gets peace. Then one chunk for household stuff which you all do together. Get DC involved in shopping, dusting, laundry sorting etc. Put on cheerful music. Get it done as a team. One chunk of time you get a baby sitter and both adults have time off together. (Usually Friday or saturday night) Then two chunks spending time together as a family doing fun stuff. Block them together for a planned day out or half a day each day of the weekend for park/Disney film/city farm etc.
One chunk of time each day for daily stuff that needs doing - the usual cooking, eating, bath routines etc, and that leaves one chunk over for shit that always happens at some point.
DH and I really worked hard at this one. The best thing about it was that we both knew we had a non-negotiable four hours to ourselves each weekend, pre agreed. It could be a night out with friends or a morning in bed, or shopping without trailing buggies and whinging DC. And we also knew we'd have a night out together each weekend. We also knew we'd work hard together as a family to do the boring stuff: clean the bathroom, make the beds. Getting DC involved made it fun for them. And they got their attention and time out too. I can't remember when we stopped needing to do it, but when DC were small it really changed weekends from grim, resentful, exhausted battles to well organised and planned fun times as a family.