I'm going to leave the main issue alone, as you've had lots of comments.
But I have to pick up on the 'lose them to their wives' 'if they divorce will I see my grandchildren' stuff.
Firstly, many grandparents (maternal and paternal) see less of their grandchildren than they would wish. For any number of geographic and other reasons. I know many mothers living in different countries from their parents and close(ish) to their in laws, for example.
Secondly, you do not lose your son to his family. The fact is that, in our patriarchal society, women often take the burden of organising the social life of the family. Setting the meet-ups, posting the birthday cards. That is why the family of the mother can end up getting preference. If you're doing the organising, you sway towards organising in a way that suits you. So you have a few things you can do:
- raise your sons not to abdicate responsibility in that way;
- raise your sons to treat women well and to treat people generally nicely, so that if they have relationships they are more likely to last and any break ups are more likely to be amicable (the woman who uses possession of her children to punish a perfectly lovely ex and his family being the stuff of Daily Mail caricature and really not so common in real life); and above all,
-be nice to any woman who has your grandchild. I know at least two sets of grandparents whose sons have gone totally off the rails and don't see their children, but by virtue of being nice people who the mother likes and trusts with her children, are still heavily involved in their grandchildren's lives.
I know you are probably thinking it is unfair that you have to put in what seems like 'extra' effort, but well, 'wifework' screws us all over in many and varied ways. And, to be honest, those are things I shall be doing too raising my girls (with an obvious tweak to the first one).