After Volume 21 is Marriage possible?

The epilogue in Volume 21 ends with Finn and Loki wanting to recruit Bell into their family but that's physically impossible since Bell hasn't reached the 1 year limit yet and Finn isn't an idiot to propose a War game against the Hestia Freya alliance since they will 100% lose.

If they just want Bell in the Familia then pretty much marriage is the only answer because I'm curious why Finn and Loki said recruit Bell into the family and not say alliance with Hestia Familia just like what Zues and Hera did?

Oh and remember there's literally no written rule against marriage between 2 members of different familias, it just rarely happens because conflict can happen on who's familia the child born will belong.