"Any advice please?"
For simple trueing you don't need a stand - that's what brake blocks are for...
If spokes break when you tighten them they were probably too tight in the first place - or just 'tired and unemotional'.
'Main' problem is if nipples are 'frozen'. If you turn them about a 1/4 turn and the spoke just twists, turn the spoke key the other way about 1/2 a turn if it's still frozen, just hope it's the only one... You may still be able to true the wheel OK with one or two stuck spokes.
Bigger problems occur if 'someone' has used the wrong size of spoke key and chewed the nipples (they are usually made of brass, which is relatively soft).