To be clear, you're getting a gift of 40k and a loan of 30k? You will repay 30k plus interest over time with a serious of annual instalments of 3k, and you will not repay the 40k at all?
No CAT liability for you on the 40k gift because it's within the 40k threshold (assuming you have received no other Category B gifts/inheritances in the past).
No CAT liablity for you on the 30k interest-bearing loan because it's not a gift (assuming the interest rate you pay is at least as high as your sibling could have got if they deposted the 30k in a bank instead of lending it to you).
No CAT liablity for your sibling on the annual instalments you pay to him by way of repayment of the loan and payment of interest because they are not gifts either. (Therefore there is no need to limit these instalments to 3k per year.)
However the interest component of the annual payment to your siblign is income, and attracts income tax. Your sibling should include the interest amount in their tax return.
If, instead of lending the money to you, your sibling put the money on deposit they'd pay DIRT at 33% on the interest earned; under this arrangement they'll pay income tax at their marginal rate which, depending on their circumstances, may be higher or lower than 33%, but in the big picture the difference is not going to be huge. If necessary you can agree pay your sibling a slightly higher interest rate so that the after-tax amount they receive is not less than what they would have received if they had deposited the money in a bank.