I have 4 kids 2 with one dads name and other two with there dads name , I wish to put my surname on the end as I am there mum would be nicer for everyone to have same name . Was never married to ethier of the men.. they don't show interest in children's lives is this OK

Where?

Let me get this straight - 4 kids by two fathers? Never married, no Court determination of paternity on any of the kids?

I'm assuming you are in the UK. But ANY question of law needs to include your general locale as laws vary by area. I would consult a solicitor. You can't just go about making changes to a person's legal name.