Support corrin or mask-lucina?

Yes for summoner and ally, Geirskogul's effect (B!Lucina) will stack.
Buffs with the text, "during combat" tell us that the buffs take effect during combat. Unlike buffs similar to Hone Armor for example, these can stack up. For buffs like Hone Armor, the unit takes the highest stat boost and cannot receive any boosts to that stat unless the next buff gives a better boost. In which case, that better buff value replaces the old one.

Sorry if this sounded strange, not the best at explaining things.