1. Bond to them when they're babies. Babies who are well-bonded to their parents can make deep personal connections to others. Babies who never bond can't; they not only don't know how, they have no idea such a thing exists.
2. Organize regular "active-attention" family activities, both work & play, without involvement of 3rd parties like electronic screens. "Active attention" means you're making decisions regarding where your attention should be, & not passively responding to something else driving it.
3. "Active-attention" rules out most family vacations where you passively participate in attractions instead of actively driving your own attention & effort towards a common goal. Though you could arrange bonding activities, like @darwinslair's family hunting trips.
4. If you as a parent bond well & relate well to them, they'll tend to bond well & related well to each other.
Being emotionally over-reactive to problems is where a lot of family tension comes from. Being non-reactive, empathetic, & gentle with them prevents that.