It's very wearing having an on-going illness and it can be so hard to stay positive. But you're getting treatment, it's luckily not malignant, and you will get over this and get better.
Your daughter is probably acting up as she's worried about you, so if you explain that you are sick now but will be better after the op, she may act out less.
My mum was in hospital for a week when i was about 7 - i still remember having all that time with my dad, and eating lots of chips, but in a way it was a special time, we all pulled together, and did a huge tidy the day before my mum came home from hospital. Your daughter and husband will hopefully have this same bonding time while you're in hospital, and it will help their relationship. You and he need to be open and honest with your daughter - you're sick and have no energy, which is awful for all of you, but you'll have an operation and start to get better, and they can help each other when you're in hospital.
And don't blame yourself, or your BMI, for your condition - it's not your fault that you're sick. It is really bad luck that you developed a tumor, it's not your fault. You can use this to kick start a healthier diet, so something positive comes of it, but your doctors have told you that it's not your fault, so you need to go easier on yourself.
I don't have any personal experience of spleen or pancreas conditions, but i do have a cousin who had to have his spleen removed after a car accident and it hasn't changed his life style at all - he has a job with lots of travel and a great social life. I'm sure people with personal experience of your conditions will be along to give you advice.
About the facial hair, i have a fair bit, especially with peri-menopause. My hairs are 90% fair but bristly, and as they're fair i can't get electrolisis, but there are lots of other options - depilatory creams for the face are great - even for the witchiest hairs! - and tweezing is oddly satisfying, while shaving is not ideal as it all grows back at the same time but i've done it a few times... It's all manageable.
And you're not a failure for being sick, bodies are not machines and they do go wrong, it's not a moral weakness to be ill.