Your concerns are very valid and I more than anything just want to say it please don't feel guilty as, hand on heart, I would say it has nothing to do with life being a bit chaotic. Both my 2 with difficulties have had waaay more attention than the 2 without due to the sibling gaps I have (21 months between 1& 2 then 5 years to DS3 then 18 months for DS4).
There's definitely enough there to warrant a full speech and language and paediatric assessment which you've got in hand. Do chase up if you don't hear back as the system is a bit prone to losing people here and there.
DS3 took a long while to take to books, and we used to role play little stories out with teddies and toys before bed. How much good that did I don't actually know, but it made us feel better about it.
When you're not sure where the level of understanding is, it makes life tricky with one, so even more with 2. Hopefully the SALT will give you some specific advice when you have your sessions. You're probably doing all things I would suggest, but it's always use words with your actions, but keep the language short. Try and join them in what they are doing and gently expand play that way. Visual supports can be really useful, but you may want some guidance from the SALT on how best to approach.
Hanen do a couple of books that may be of help, It Takes Two To Talk and More than Words. The latter is more focused on ASD but is a good resource for receptive language delays. Both of them are v expensive! But tend to be recommended by SALTs. There was another book I read for DS1 but it's totally gone out of my mind. I will report back if it comes to me!
I'm glad you're mum is supportive and coming round, hopefully your husband will follow suit asap. It must be so very overwhelming atm, so go easy on yourself too.