Thank you! Looks like I meant the HMS Victory in the historic dockyard you mentioned.
I thought as much. When you leave the ferry port you have two choices, either walk to the Historic Dockyard which would take about 30 minutes but it's through a pretty deprived and unattractive part of the city (much of it is!) although Chrles Dickens' Birthplace is situated en route surrounded by Ugly apartment blocks and bail hostels. The more preferred option is to take a taxi or Uber. Aquacars is the largest taxi operator in the city and has the largest fleet of vehicles +44 23 9265 4321 or there is an app that you can download and use in a similar manner as Uber. The journey should only cost around £5 so it might be easier to split the group and take two taxis.
Entry to the Historic Dockyard includes access to all the sights with the exception of the new Mary Rose museum and can be expensive for a large party such as yours. Unfortunately you cannot pay just to access HMS Victory as once you're within the Dockyard there are few places that check your ticket. It's a whole day affair so to arrive at the Ferry port at 1:15pm doesn't leaveyou with much time to explore the dockyard before moving on to London for that night plus fitting in lunch somewhere.
There are few places in Portsmouth to store your luggage however I've found a scheme called BagBnB which provides safe and secure places for you to leave your luggage for a fee (https://bagbnb.com/luggage-storage/portsmouth) the closest and most convenient location is near the Portsmouth Museum. The site won't reveal the exact location until you proceed with the booking process but they state that it is at a hotel close to the Portsmouth Museum and the Ernest Smith Clock Tower for which the most obvious conclusion would be the Holiday Inn.
The Holiday Inn is located in Southsea opposite what is called Southsea Common, a large expanse of recreational ground forming a promenade that was the highlight of the Victorian seaside resort. It is a short walk to Portsmouth Harbour train station and also historic Old Portsmouth. Here you'll find cobbled streets lined with old houses and taverns, ancient fortifications and an area called The Point which is where many ships left for battle or for prisoner transportation etc. It's a fantastic spot for watching the ships and other water craft entering and exiting the harbour and there are two pubs next to each other, The Still and West and The Spice Island Inn (the area was previously known as Spice Island as it was where the spices were brought in from around the world), both pubs provide reasonably good pub food and combined with the views make for a popular place to have lunch.
I would recommend taking a taxi from the ferry terminal straight to the Holiday Inn to store your luggage (if it is the hotel the wesbite vaguely refers to) and then walk to The Point for lunch after which you can head towards the Esplanade along Broad Street then Battery Row which will lead you to the Royal Garrisson Church, a 13th Century church that experienced significant damage during The Blitz. Carry on towards Clarence Pier, a rather dated fun fair reminiscent of Atlantic City's Steel Pier which you may choose to pass on by or the kids might be tempted.
Further along the Esplanade you'll find the Blue Reef Aquarium, The D-Day Museum and Southsea Castle, built by Henry VIII and from where he watched the Mary Rose sink during battle.
This would be a pleasant way to spend a few hours in Portsmouth before taking the train from Portsmouth Harbour to London.
