Wedding question

Megan💟🌻🎀 • I`m 21 y/o. Army Fiancé We have been together for 5 years. TTC Baby #1
So my fiancé has 3 sisters and 1 brother. He's told me that his brother will be in it and his best friend but doesn't know who else will be. I have 3 girls already but I feel like if I don't ask his sisters it will cause drama. But his family was never too fond of me so there's been drama in the past and he always told me he loves me and doesn't care what his family thinks of me. He is currently in basic training for the army and there was drama with his mom and I when he left so it's not exactly a good relationship with his family and I don't want to make it worse but I don't want a big wedding party.