My dad has a 10 year UK visa, on the remarks it says "family visit" my question is if we go on a vacation to the UK will it be a problem for him ? can they refuse him entry?
On 24 April 2015 all existing visitor visas, including family visitor, business visitor, student visitor, child visitor, and others were automatically converted to the 'standard visitor visa'.
So yes, your father can go on a vaction to the UK or do any of the other activities listed in Appendix 3 (Permitted Activities) in Appendix V of the rules.
The controlling link if you are interested is the Immigration Act 2014.