I see there is a bit of a bunfight, which is regrettable.
As the mother of four DDs and a DS with a bright future ahead of them that depends on going to university and doing well there, I can see where your opposite numbers are coming from if they are angry. On the subject of Catholics in general, most are not so conservative and I don't think this is where their anxiety is coming from. Any parents of a daughter with 6 more years of university to go before qualification would very realistically see a daughter's future and hear a loud sucking sound as it all went down the drain when they heard the announcement of a pregnancy. The fears of the other half here are probably based on real perceptions of how the burden of carrying a baby and caring for one usually fall on the mother. That is true no matter what religion (if any) the mother and her family have. Of course they may have some notions of their daughter now becoming a 'good girl' SAHM and throwing her education away. I hope your DH's positive and forward-looking attitude will help everyone see that there is a future graduation and professional career for this young woman as well as for your DS.
Raising your daughter to be compliant and a 'good girl' (which can happen in any family where mum kowtows to dad) often means raising your daughter to make huge mistakes and try to please everyone when it comes to contraception and taking charge of your fertility when in a relationship. That is a personal observation of some 'good girls' who have been put in an impossible situation, never taught to put themselves and their own best interests first, in other words, not prepared for real life and real responsibility. Charting, etc., is much more useful as a way of planning to have a baby than to avoid having one. It is not what responsible unmarried women who cannot support themselves financially should rely on in order to avoid pregnancy.
On the subject of marriage, I see no reason why they could not get married if they wished in a RC church, unless there are rules where you are that are a far cry from those in operation where I am. That is if they wish to. There is no guarantee that they will stay together or want to take their relationship to that level.
A family I am friends with have two DDs, one of whom had a baby at age 17. The young mother went to university while her parents took in the baby pretty much full time. The condition was that the mother would fund her own studies because her parents could afford to either take care of the baby or pay for university but not both. Two degrees later, the 'baby' is 11 and living full time with her mother who is a professional working full time, married to a new man and the mother of a 2 year old DS who was born during her final year of professional studies.
When this baby was born the husband's mother travelled and stayed three days and nights to take care of her grandchild, and the grandmother who is my friend did the other four days/nights of babycare. The mother arranged her classes so that she travelled three hours to her university on a Sunday night, stayed in a rented room, went to class for three days solid, travelled back home late on Wednesday, and did her studying and assignments for the other four days. Without her husband's salary as an anesthetist the expense of all this alone would have made it impossible. Without the willingness of both grandmothers to do their shifts the expense would have put it out of reach as they would have to have hired a live-in nanny. The father worked hospital shifts and babycare by him was out of the question.
The mother's older sister had her first baby (with her husband whom she married at 6 months pregnancy) during her second last year of medical school, and her second baby while a hospital resident. The grandmother moved to this daughter's city to take care of the first baby for his first four months when he was a newborn and when the couple and their baby moved closer to grandparents she took care of the first grandchild as well as the second and then the third. I took care of the oldest grandchild during the day while the grandfather worked, and he would pick her up and give her dinner, bathe her and get her off to bed. After breakfast he dropped her off at my house.
There may be similar heavy lifting in your future. Of course, it may well be that the grandads and fathers involved here may take up the burden, but is this how they see things? If you think you will end up bearing more of a burden than the men involved then maybe you can think a little of the parents of the DIL and understand their concerns.
Finally, congratulations. My friends love their grandchildren to bits and they are wonderful children, cherished by the extended family to the point of idolatry, and their daughters have wonderful careers.