Living space alone is a necessary consideration. Eternal population growth is unsustainable,
Speculating potential fixes could include:
Retrospective expansion or adjustment to the Earth/universe
Infinite Multiverse Colonisation
I'm not an expert on the happily ever after on earth religions but in talking to their members, I get the impression that Sterility would ruin the whole 'Family life is everything' concept. Unless you also freeze aging for the kids, it means the end of it. What would they do when the kids grow up and leave? The Eternal Cleaver family solution where the Beaver never grows up?
The 'Expandable Earth' concept would work and I suppose the adjustment of gravity laws when the mass gets to be too much would be possible for God. Or maybe bodies could transform to have titanium bones and hydraulics for muscles to compensate for the increased gravity.
The Infinite Multiverse thing is appealing but isn't that just another concept for Heaven? For some reason they don't see themselves fit for it. It seems like a bridge too far for those who see themselves carrying on like they do now but on an idealized New Earth,
The real problem in my mind is that when the real-estate problems are solved, even in the most ideal of families, won't the women ever get tired of being baby factories? Won't men get tired of the responsibility for the physical and emotional upbringing of an endless string of children? I did it twice and it was grand, but for eternity? Sounds like hell.
And then there is the fairness question. How come all these new kids get a free pass to eternity without making it through this **** storm on old Earth?
I just don't think they've thought it through.