If you have a good relationship, ask him!
It would be unreasonable for him to deny access by your parents to DS. If ex is uncomfortable with your friends, DS could always see them with your parents until he is old enough to be taken out by the friends? (Ex may appreciate the break from DS, depending on his work and social commitments)
In turn, you should point out to ex that, should he die, you will honour his requests for DS to see ex's parents and friends.
As for the house, if it was your original home, it might not be a big deal for him to move back in!
If your relationship is not so good (and it seems a shame, as you are offering something to him as well), it might be a matter for a family law solicitor before the will is drawn up. However, hopefully it will not be necessary!