Who can submit form SEV?

My mother and her partner wish to sever a joint tenancy, and revert to tenancy in common on a property which they share. To do this they plan to complete the form SEV, and also send a notice of severence between them. 

My question is in reference to panel 6 "Can I, the son submit the form "SEV" which they have completed and signed?"

It would be easier to manage any issues relating to requisitions if they happen, as both the owners are a little old and not the best at dealing with admin.

Matthew - you may

Thank you