I wear a different brand of hearing aid but many brands offer what’s called a “TV Streamer.” The streamer takes audio input from the TV and sends it directly to the listener’s hearing aids. It involves additional expense to purchase the streamer but if you can afford it and it’s offered for your make and model of hearing aid, it has several decided advantages.
A main advantage for the aid listener is the pure audio from the TV is directly reproduced in the listener’s ears. Room noises and reverberations of the TV sound in the room are greatly reduced. The user can control the amount of streaming vs. the amount of surrounding sound he/she hears from within the room via the external mics on the HA bodies. Another advantage for the HA listener and normal-hearing people in the room is that the TV audio can be split, so some goes to the normal TV speakers whereas a separate channel goes to the HA listener’s ears via the streamer. This allows the normal hearing room listeners to adjust the room speakers to a volume more to their own liking; same for the stream going to the HA listener. In my case, the audio came out of the TV and went to an amplifier via a TOSLINK digital audio cable. I bought a powered TOSLINK splitter on Amazon and some additional TOSLINK cable so one branch from the splitter goes to my TV Streamer, the other branch goes to the amplifier same as the original single output cable. My adventures in setting up my streamer are described in the following thread: Does It Make Much Difference What Type of Audio Output Is Used for TV Streaming? - Analog vs. Coaxial vs. TOSLINK S/PDIF? Other folks on the forum have had similar experiences. Most people love the streamer and think it’s worth the money and effort to set it up, especially if there are other people who want to listen to the TV at the same time.
Perhaps someone can weigh in on Signia hearing aids. It should be possible with a reasonable seating arrangement and good room audio characteristics to get decent TV sound direct to your father’s HA’s without investing in a streamer. For me, though, I do find speech decidedly clearer to understand from the TV when using a streamer as opposed to listening to TV sound directly with some of it bouncing around the room. Does the TV audio sound great and crystal clear to normal hearing folks, too?