Guarantor legality?

Hi

My daughter has an AST agreement on which my husband is named as Guarantor. The AST is 5 pages long, and the Guarantor's obligations are set out in 'Appendix 5' (not a deed). The landlord has not signed the agreement. My daughter and husband have signed but the signatures are not witnessed. The Tenant's, Guarantor's and Agents initials are on the bottom of all 16 pages, but not the Landlord's.

My questions to anyone who may be knowledgeable enough and kind enough to help are:

1 Is this legal?

2 Regarding posts I've seen about 'consideration' in an agreement - the first paragraph in Appendix 5 says "In consideration of the Landlord agreeing to the Guarantor's request to accept the Tenant as the Tenant of the Premises upon the Terms and Conditions of this Tenancy Agreement the Guarantor agrees that if the Tenant default to 1) pay the Rent as it falls due and 2)fully compensate the Landlord for any loss, damage, costs or other expenses arising either directly or indirectly out of any breach of the Tenancy Agreement" There are several more paragraphs of obligations! Do you think that this is fair consideration?

Thank you