First of all, you must ask yourself if this is a viable business. Personally, I doubt it is. The transaction costs in Ireland are so high, that they will eat into most of your profit. Stamp duty of up to 9%, legal fees on purchase and sale and auctioneers' fees on the sale.
In the examples I saw on programmes on TV such as property ladder, the profit was made simply because the properties went up in value. If they had bought the house and done nothing except sell it 6 months later, they would have made the same profit. In England, the stamp duty is much lower - usually around 1% I think. And you can do your own conveyancing in many cases.
In calculating your profits, you must factor in the salary which your brother in law is giving up and any time which you put into it.
There is a serious risk that house prices may fall during your period of ownership. You must make a comfortable enough profit to compensate for this risk.
Do not use a company for property development. The tax disadvantages are very high.
You will have to try to structure it in a way that the profits will be subject to Capital Gains Tax. But I think the Revenue will regard you as trading, so you will be subject to Income Tax.
You should do a separate partnership agreement for each property you develop. The banks will lend to you if you have security. If you don't have plenty of cash to pay for unexpected problems, I don't think you should do it.
brendan