The SQ, AC and UA lounges are in the satellite terminal, your LX flight is out of the main terminal. After passing through security, you'll be in the main terminal.
The LH lounge in the main terminal is much less of a walk than the lounges in the satellite. With an elderly companion, I'd say it takes 15-20 min to get to the satellite lounges. There are some electrified pedestrian walkways on the way to the satellite. They only got those *towards* the satellite. On the way back, you either need to walk all the way or wait for a golf cart which drives you back. The golf carts are for passengers requiring assistance, elderly passengers and such. I don't think it would be a problem for you to get a cart.