Walburga had always been a cold,reserved woman..she's never been much of a talker or an affectionate person overall. With her children,she was especially rough. Sirius and Regulus were her biggest love and disgrace,love because she couldn't describe the strong connection between them,disgrace because that love was her misery. When she found out she was pregnant with her first,she had sworn to herself to not let herself feel an ounce of love.. Just raise them as heirs. Proper boys. That was her job.. But damned those feelings,she couldn't help it. That's why she had to act indifferent to them,and hurt them as much as she could,so that they would distance themselves from her.. Save them.