The Structural Engineers Pocket Book summarises some recommendations from the UK's National House Building Council (NHBC).
I will assume the tree has a moderate water demand and a high plasticity for the soil. In the current condition the D/H ratio for the trees is 4/6 = 0.67 and in the final condition when the trees are 14m high the ratio is 4/14 = 0.28.
Checking against the chart for high plasticity soil the depth of influence for the current condition is 1m (this is the minimum for this type of soil in the UK) and for the final condition is 1.3m. In principal, provided your building foundations are deeper than these then shrinkage caused by drying out of the clay due to the trees roots should not be an issue. This is of course based on local practise and so it would be worth getting checked out by a local professional if in doubt. This shrinkage is typically the biggest issue for structures in the UK rather than root damage, although given time roots can cause problems. Conifers tend to have deeper rather than wider root systems though.
Regarding protecting your house, it will somewhat depend on the layout of the house, the structure and the design of the foundations so you will probably need to seek professional advice. One point to note with regard to cutting the trees down, this has been known to cause as many problems as not cutting trees down because as soon as you cut them down you reduce the amount of water being drawn from the clay causing swelling. Because these trees are relatively new, this shouldn't be an issue but may be something to beware of.