Days to have kids - awkward ex GF

Good afternoon,

I am looking for some advice from this wonderful community.

On the 5th of February this year. Me and my children's mother split up. We have three children 7, 5 and 3. I left with nothing, got myself a lock up, gathered pieces together and lived with my parents for 2 months. During this 2 month period I also had them as much as I possibly could at parents. And I did the school run every single morning. I now have my own house, 3 bed fully detached, nice gardens, and additional play room. I went for a property of this magnitude for the reason of the children. If I didn't care then I would of just stayed at my parents spare bedroom or got a one bed flat etc.

Since moving into the property (may 6th) I have had the kids as much as I physically can. May was 11 nights, June will be 12, July 12, August 13 nights. Up until last week I was still going over to my exes house every morning to do the school run. She has since stopped this after a massive blow up, she placed pictures of new girlfriend on social media and false accusations. I have since had her brothers messaging me threatening to smash my face in. I am no longer allowed to her house.

I work in the horse racing industry, and have done when we conseived all three children. She's always known my job. I am extremely busy in the summer but less so in the winter. Average 20 days April to August. But 10 days September to March. It is what I consider a well paid job and its all I've ever known. Do to the nature of the business, Saturdays off are very few and far between, maybe one a month. Yet she is persistently hounding me to have weekends off. My arguement is that, my boss would then get rid of me. I'd have to take a job which pays 15k less and will probably be Monday to Friday 9 to 5 and I would probably see the children less and would have to move to a smaller property. The gov guidelines dictate 170+ days a year is deemed 50/50. I fully intend to have them 170+. My question is.. is there anything legally that states what nights of the week/how many weekends?

I currently also pay her £250 a month for the children, should I be doing this? She receives benefits, works certain hours and lives in a house half the cost of mine. I call the kids every morning and every night to say morning and goodnight. Although she barely answers these calls anymore. 

She is one of 10 siblings and they are somewhat unsavoury. I think only 2 of them work. The rest are drunks, spongers, drug addicts, in and out of prison etc. Whereas I'm an only child and I feel somewhat ganged up on, and always have done.

My ex nor her family will let my children see my new GF. I just want to move on with my life, have the kids as much as I can and move on peacefully. I just feel like I'm under so much pressure trying to juggle everything and keep everyone happy in life. The past few weeks I've had massive panic attacks, to the point I thought I was dying. 

I love my children with all my heart, yes I'd like to see them more in the summer but I'm doing all I physically can right now, but just seem enough.

If somebody has any advice, I would be than grateful.

Kind regards. Thank you in advance