I could have written your post. We all were enlisted into emotional caretaking BPD mother- and my father was her enabler. I agree with having some boundaries on your doing this as an adult, but how you go about this, and the reaction from your parents and other family members is something to think carefully about. My experience is a cautionary tale.
I had perceived my BPD mother as the one with the problem and my father as the nice good guy, victim to her behavior. This wasn't accurate. He also was a part of the dynamics between the two of them, a dynamic that was more complex than I realized. Your parents have been doing this for years. This is your father's primary relationship and focus.
Read about the Karpman triangle dynamics.
https://www.bpdfamily.com/content/karpman-drama-triangle. This helped me to have a framework for the behavior and relationships in the family. BPD mother ( and I believe this is common for pwBPD) was in victim position, Dad as her rescuer. Any perceived threat to BPD mother- real or not- the two would bond together against. BPD mother perceived people as being
"on her side" and "not on her side" and Dad would be on her side. Any distress on her part- real or not- Dad would step in to appease- similarly to finding the college classes and complimenting her as with your mother.
It may appear otherwise but Dad wants this rescuer role as much as BPD mother sees herself as victim. Your father isn't a victim. He's a part of this, even if it is difficult- he could choose to have boundaries too, but he doesn't. I eventually understood his role better when I did work on my own co-dependent/enabling tendencies- these were behaviors that I was raised with- but wanted to change.
Next, look at family systems. I don't have a specific article to post but reading about it I saw that families operate as a unit. If there's a disordered person in the family, other members take on certain roles to keep the family in balance. The roles may be disordered too- like children being enlisted as co- emotional caretakers- but they are functional within the family unit. If one person changes their role, the other members will feel discomfort. First, they will attempt to get the "offender" family member back into their role. If that isn't effective, they may then oust or exclude that family member and form a new balanced family unit. This may help explain the behavior of other family members when you consider changing yours.
I think you are on the right track with your own therapy and how you interact in relationships. I have done this too, and also with attention to enabling behavior and boundaries. All this is good work. However, keep in mind that you have had some recovery and are interacting in new emotionally healthier ways with people, you know better, but your parents, and also possibly your siblings, have not changed.
So back to boundaries- yes to boundaries but "pick your battles". I did have boundaries with BPD mother- over the boundaries that were important to me. One was that she was beginning to enlist my own children as emotional caretakers to her. She could be verbally and emotionally abusive. Protecting my own kids, and my own emotional well being was a boundary to keep.
The other was Dad's well being. He got sick and she was in charge of his care. I intervened thinking I was doing this in Dad's best interest. What actually happened was that I unknowingly stepped into the Karpman triangle, which I didn't know about yet. I also was stressed, upset myself, and emotional over the situation. I loved my father and thought we had a good relationship but the dynamics with my mother were stronger than anything else.
BPD mother disliked boundaries. She was angry at my having them. I did have words with her, something I usually avoided doing as it resulted in her reacting even more but we don't have as much self control during stressful situations. A "normal" parent would have understood that the situation was difficult for all family members too. But BPD mother, could only see the situation from victim perspective, and she reacted. Dad took her side "against" me. She rallied other family members to her side as well.
What I didn't realize until I naively stepped into this dynamic is that- the whole family system relied on each of us maintaining our roles. If we didn't- BPD mother reacted and the result, is that this increased Dad's discomfort in the relationship and he felt the need to fix it. The very same dynamic you see if your mother has an issue, real or not, she reacts, Dad becomes uncomfortable, steps in to fix it- and also enlists others to do so.
I don't regret having boundaries with BPD mother. They were necessary. I don't regret standing up for my father's well being, but I didn't realize how much of a reaction that would elicit. If I were to do it differently- it would have been with more knowlege of the dynamics in their relationship and family dynamics, and also how my own emotional reaction to BPD mother added to the drama in ways I didn't imagine.
My mother's extended family would compliment her like your father asked her too. It seemed strange to us- they'd rave about her doing what we think of as ordinary things as if she did something amazing. But there was the same imbalance in the family as yours. BPD mother did attend college but her extended family members had careers and she didn't. I don't know how aware they were of what they were doing but somehow they knew that this helped to keep the peace with her.
My best advice to you is to have boundaries but pick your battles and know that what you are stepping into when you change your behavior in the family could be bigger than what you expect. I don't suggest you continue to have no boundaries and appease your mother- but to proceed with caution.
This also depends on how close you live to your parents and how often/long you visit. Sometimes going along with the dynamics and not rocking the boat over a short visit is the path you want to take. Sometimes holding a boundary even though there will be a reaction is necessary.
You decide but know, your parents aren't going to change their pattern. Still, you have changed your behavior for the better, and are going to change the cycle for yourself, your own relationships, and that is a good thing.