Proof of work experience

I am claiming work experience in fathers business. 14 months between my bachelors and masters and about 2 1/2 year after masters. I have IT returns for previous two years (salary in cash). Experience before masters I do not have any documents. Should I get form 16 as proof? Also, few months into my work, I went to UK to attend my graduation ceremony. Can I claim these three months in paid leave?