If these two were born as you say, then there is no way they could be brother & sister.
One born 7th July 1917 does not leave mum enough time to conceive and give birth on the 15th January. A birth in 1917 meant that mum was in hospital or at least laid up for usually a week to 10 days. If we use the shortest rest time of 7 days, it leaves 185 days to get to 15th January.it gives 26 weeks + 4 days or 6 months.
This would give mum a gestation period of barely 6 months, and without today's technology the baby would not survive. that is why I think they are not brother & sister, Maybe they are cousins.