Dreamerb has really told you the problems you have here. In reality, you know the house is worth 850K. Stamp duty is payable by a purchaser on the market value ( 850K) NOT on any other deemed/wannabe value.
Contents contract is a non starter - it is obviously not a real situation - even where contents come into it Revenue will not readily accept a contents situation of much more than max 10K - if that.
To avail of the consanguinity relief you will need to have the Deed adjudicated and Revenue will require a reputable valuer to furnish a valuation for the property. Go in with a dodgy makey uppy valuation from a "makey uppy auctioneer" and your feet will not touch the floor for Revenue going through you for a short cut. Most valuers will not touch a low valuation situation. Their neck is on the line.
1) Say the market value of 750k on the house is got as is legitimate
Its not.
2) Parents gift the land value of 150k to me
Its a scheme, part of a series of transactions, won't wash.
3) I pay them 600k for the value of the house now
No problem with this.
4) I pay them 50k for the contents contract
Won't wash.
As stamp duty is only paid on the consideration then i would only pay 3.75% of 600k.
As above, duty is paid on value ( 850K)
From my parents point of view I will pay them 650k now and in 10 years on an unrelated matter would gift them each 49k (within CAT)
Well you could do this but then on the face of it - they are gifting you 200K now- unless they have a protection by way of a legal agreement, you may not pay the balance. And since the purpose of the legal agreement is to avoid tax, it won't wash either.
Finally, as you will be getting a mortgage, your lender will want to make darned sure this is all done above board so that they have recourse if you default so they will tie you and your solicitors in a knot of compliance issues.
Why not just pay the half rate stamp duty? Thats a great deal.
mf