MIL drama ahead of wedding

Our wedding is in 5 months. MIL doesn't want her ex husbands gf there - we let her win and told FIL he was invited alone. Now she is kicking off about the ex husbands family, how they shouldn't be there. To elope or not elope? I sense drama on the day and am in two mind

EDIT: thanks for the responses - very useful and appreciated. We chatted about it this morning and he is clear - understands the situation with the ex because of historical reasons in their family but is going to be clear when we see her tonight - "this is OUR wedding, if you/anyone elee wants to share the day with us then accept our decisions"