Relationship breakdown between tenants

Guarantor

I have an unusual situation. We have a couple whose tenancy is backed by a guarantor. They have had a falling out [quite serious] the boyfriend has been arrested but part of his bail conditions state that he cannot return or go near their home. Now the guarantor is the boyfriends father and he is not not willing to remain the guarantor for the property if the ex-girlfriend continues to live there. On her own she does not meet the affordability criteria and cannot show any proof of earnings / income. The boyfriend wants to return and continue to live in the property but can't while she is in residence. They are 2 months into a 12 month tenancy. Is there anything that we as managing agents can do in this situation? Is it simply up to the tenant to seek legal advice? and can the guarantor withdraw his guarantee from this agreement?