I do not think the two are related. Tensi and tenta are transparently the prefix ten (cf. tenna) "towards" + the demonstratives si "this, here, now" and ta "that, there, then", so tensi means "up to this point in time, by now, still, already", and tenta is "up to/by then, still, yet".
The endings in entu/ensi/enta look gender specifiers to me.

Thank you, Tamas. You clarified the meaning of tensi/tenta. I misunderstood the layout of PE22:157 as saying the root the came from was √TIG. Would entu/ensi/enta have the prefix en- yonder, therefore giving the meaning he/she/it yonder (of course now realizing the later forms may be ento/ente/enta; -u > -o, -i > -e)?

+Jim Coish well +Christopher Gilson in VT36 certainly argues that en in these forms is probably the element 'that yonder' and the second element is the demonstrative ta with gender specific forms. However, I think declination for gender was largely abandoned by Tolkien later.

I think they were perfectly attested in PE15:054, 057 as, apparently, m/f/n emphatic 3sg. pronouns. Per Gilson, ' en- [here is] described in EQG as "a general demonstrative deictic particle or stem added to the demonstrative pronoun stems for emphasis".